You realize that humans are simple minded creatures and big names are hard.  Then you get over your self and it dawns on you that people aren't mind readers, no one automatically knows that Alexander really goes by the gender neutral Zan, or maybe Xan or Zaughn.  

If this is your biggest problem then I envy your life.  

BTW I have a name that everyone turns into a nickname. I stopped caring a few decades ago and just answer to everything now.  "Yo b*tch" me, "Yeah?"  

This is genuinely frustrating and quite disrespectful actually - but I think people don't MEAN disrespect by it, usually. 

I have a name that my mother thought couldn't be turned into a nickname, but people still managed it. I'm particularly pleased by what my rugby team did with my name. It could have been sooooo much worse. (There was a girl called Giz, pronounced jizz.)

Just keep telling them it's "X", thanks.

I have a long name too.  Some people shorten it to the nickname I'm not too hot on but it's not a big deal.  In the grand scheme of things...it's just a name.

My DH named is eldest son a name that can be shortened.  Then gets p*ssy because everyone shortens it.  Well, then, ya should've named your kid Dean or Lee or Mark, etc.  Even then people will give you nicknames.  My DH's can't be shortened but I call him a petname so much that his real name seems weird.

Being in the military for many years you NEVER adult by their first name, except among friends and not in front of anyone else.  Whether it's a doctor, nurse, custodian, secretary, patient, it was always Dr/Miss/Mrs/Ms/Sgt/LT Smith, Jones or whatever. So I'm gradually getting used to it but I would never assign a nickname.  Seems more commonly now that people want to use their more formal names (William, Alexander, Patricia, etc) and not a nickname.  

I have the opposite issue. I have a long annoying French name. I haven't used it in years... Even my work info uses my different name.

I know it's a telemarketer as soon as they butcher my full name. Lol

It is rude and oblivious when someone says, "Hi, I'm Elizabeth!" and someone else says, "Hi Beth!"

Just say, "Oh, I go by Elizabeth!" and repeat as necessary.  Some people are oblivious.

I understand why a Liz doesn't want to be called Beth, it's a completely different name. I will say though - an Alexander who goes by Zan has to expect to be called Alex. People are going to assume.  And if your name is Steven and people call you Steve when you prefer Steven, sheesh, get over it.  Just say, "I prefer Steven" once and let it go.

My DH's father gave all of his kids names that can't be shortened or have a Y added to them for this very reason.

Suggestion on what to do? 

Try calling them the wrong name (any ol' name). If you feel this strongly about it, make your point. 

I have to say it doesn't bother me. My grandmother called me Elizabeth for almost 30yrs. My name is not Elizabeth nor anywhere near it. Elizabeth was my mother's sister's name. My father called me a short male version of part of my name. He's the only one who did. I call my youngest son by his middle name. Always have, always will. No one else calls him his middle name. 

But all my examples are family calling me something besides my full first name. I can't say other people I've worked with and/or were casual friends with called me anything but my full first name. My first name is easy to say and to pronounce, my last name is not. If I got offended each time my last name was mispronounced I'd live my life in a tizzy.

People do that to me all the time

I have a slightly unusual name.  While there are some people that also have my name.. or a similar one.. the spelling is different with mine.  My name is constantly butchered both with pronounciation and with spelling.  But, it's been like that my whole life.  I really try to not take offense where no offense is meant.  People may be misreading my name.. or mishearing it.  The spelling my way is correct for me, but others spell it differently..there is a different origin to the two names that are pronounced the same. 

When do I make a point of correcting people?  Usually when it is someone that I am going to have a longer term interraction with.. I will correct them a few times.  We had a neighbor that kept replacing the R in my name with an L and after repeatedly correcting me.. I started calling him Klirt instead of Kirt..he thought it was hilarious.. but still mispronounced my name..lol.

Otherwise... for transient meetings... I just don't bother with it.  I know they don't mean to make the mistake.. I let it go.

As to why people shorten some names.. I would say that a majority of people with some names use a shortened version.  Most Thomas' go by Tom or Tommy.. Most Robert's go by Rob or Bob.. but yeah.. not all.  In a work setting, I use the formal until I see them signing their name back a different way.. or hear someone else refer to them by the shortened name.. or if they, themselves introduce themselves as the nickname.

"Hi, can you please put a different name on my account? I prefer being called Zan, not Alexander. Please update your records. Thank you."

One thing with shortening names... you could be calling someone by a nickname that they find offensive or that is the name of someone else who has made their life hell. There is one nickname that make me cringe every time I hear it. It's involuntary and is the name of my psycho exh. I could go the rest of my life without hearing that nickname.

I have a friend named Allison. People are forever wanting to call her Alice, which she detests. You can call her AL or Allison.

You know that I know your pain, sweetie. When they shorten it to one syllable, just ignore the arseholes. xoxo

and yes to what Aniki said... it’s because of how someone used it in the past coupled with the fact that it means something dirty in another language. I’ve written here before that ex-sd  used to called me by the nickname, which I found utterly disrespectful after she was repeatedly told to call me by my full name. Just rude.  Three syllables was too hard for her... my 7 letter name was too long according to dad. Point is, call people how they introduce themselves, and as the relationship progresses, ASK them if you can shorten it... if they pause or give you a story, you’ll know what to call them.