I'm not allowed to see my cousins?!!!!?

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Okay, well my family life is very confusing I will try to make it short.
So, My parents are divorced have been for 6 years, My mother got married to another guy 3 years ago. I don't talk to my father and I haven't for years! But I have cousins on his side that I talk to all the time, The thing is my step dad won't allow it, He is controlling, I've never met my cousins before and he won't let me, It makes me upset that I can't even spend time with them nor talk to them without him or my mother having a go at me.
I'm not even allowed to change my last name to my REAL last name on fb It has to be my mums and step dads last name, Because apparently if I do that it's stabbing him in the back?What can I do to make them understand my point of view?