mum abused me, but, is now denying it. what do i do

hello all, i had this massive knot in my hair. so, my mum went out to buy a tangle teeser, so that she could try and fix it.
then, my mum started brushing my hair and was pulling a lot. she was brushing rather manically and it hurt so much, I was screaming due to how much she was hurting me and the pain was absolutely awful. i then started having a panic attack, i get panic attacks when i feel like i am in a situation that i cannot escape... so, as my mum is pretty demanding and wouldn't let me escape when she was pulling my hair... i panicked. i was screaming due to how much she was hurting me.
then, my mum threw the hairbrush bristles first at my back really hard, it hurt so much. the mark that the bristles made is still etched into my skin. my mum chucked the brush at me to stop me panicking and crying.
obviously, my immediate reaction was to escape, i curled up into a ball on the floor and tried to calm myself down. next thing i knew my mother picked up the brush again and this time chucked it at the window, causing me to cry out in horror, since i thought that it was aimed at me. apparently, it wasn't.
i managed to escape my mum as she was saying that my panic attack was deliberate... it so wasn't...
however, i went downstairs again and showed her the mark that the brush had made on my skin. i said that she had caused that mark by throwing the brush at me and of course i wanted an explanation. she seemed to recoil back in horror and demanded that she had not in fact thrown the brush at me, even though I distinctly remember her doing so! she then said that i was self harming and had obviously caused the mark myself! apparently i had leant back against the brush when she wasn't there!
so, we went back to the room as my mum wanted to check that the brush had moved (to support her theory!) however, i had used the brush to tie my hair up because it was a very hot day and so it wasn't in the exact same place.
now my mum is being really annoying and ignoring me, saying that i should he apologising as she didn't do it apparently (according to her!) she says that she is certain that her side of the story is true, but, I am certain about mine too!
i am sorry, but, you never forget the times where your parents hit you, nor do you forget the pain it causes.

i don't want this situation to ruin my relationship with my mother, usually myself and her get on well. this is the first time in which an altercation like this has occurred. i am trying to suggest to her that we 'forget' about the situation, since neither of us are willing to back down... but, she isn't responding!

what do i do? i am certain that i experienced the abuse and i am not prepared to back down to her manipulation and lies!