I was always called by my full name, growing up, because my parents, in particular my mum, disliked the shortened version of my name. When I left home and started my nurse training, there was another girl in my set with the same name, but she had always been called by the shortened version, so it made sense for me to carry on being called the full version, to tell us apart.
However, after I qualified and had worked as a nurse for a few years, I decided to leave nursing and go to university, and on my first day there, I decided that, as part of this new start, I would change to being called by the shortened version, and I really liked it.
Long story short, I have been called by the shortened version ever since, and it feels so much more me than the full version. My mum and sister still call me by the full name, though, and when I asked my sister if she thought she could ever call me the short name, she replied no - point blank refusal. I've never even dared ask my mum - but I am 100% sure she would refuse.
It does irritate me a bit that two people who are so closely related to me, think that they know better than me who I am - but as I don't see either of them very often, it is a minor irritation, and one that doesn't really impact my life.
If someone I was seeing regularly and frequently was to refuse to call me by my chosen shortening, I would be annoyed and would tell them so!