I split up with ex when ds was about 2 for the next 18 months xp didn't take up the contact that was offered. During that time, I legally changed the surname of my ds as I was sick of being called Mrs X (his name not mine).
When xp did eventually decide to come back into ds' life he refused to accept the name change and even now 5.5 years later sends christmas cards etc with his name on them. He has no need to post anything as he regularly sees ds now but it is for my benefit not ds'. Needless to say, I ignore it.
yanbu imo just don't give him the satisfaction - rise above it, your dd knows her name.
Well. I inadvertantly changed my nephews name. And I feel very lucky my sister didn't kill me, or at least maim me for life. Dnephew's name is Harry and my sister and her husband nick named him Ree (which if I'm honest I hated) so I called him Haz once or twice, he then informed everyone his name was Haz not Ree.