A nickname you hate doesn’t have to stick. Stop answering to it.

Names survive because they keep getting a response. Every time you look up, laugh or reply, you confirm that it works, and a group will use whatever gets a reaction. Removing the reaction is slower than making a scene and far more effective, because there is nothing left to push against.

Pick a week and simply do not answer when it is used, then respond warmly to your actual name. Introduce yourself by that name to anybody new. It feels awkward for a few days, and then you notice people have quietly adjusted.