Hi you have done the right thing to contact me.
It sounds like you felt very upset when your mum did not believe you and no-one deserves to be hit on the face or made fun of in this way. Your mum's behavior is not acceptable.
You don’t say how it is normally at home between you and your mum. It seems your dad looked after you well on that day. How would it be to try and talk to mum and dad about how you feel, or someone else you trust? Tell them what it’s like for you not to be believed when you speak with mum. You could even write this down if you find it hard to talk about.
If you would like you could come and make contact with ChildLine either in 1-2-1 chat or by phone on 0800 1111. We are always here to listen to what you have to say.
Take care
Sam