dealing with agressive behaviour and defiance

Hi just wanted to hear from other parents.  I am really frustrated at the moment.  My 9 year old who has Autism hates school hates his teachers.  He tells me that he has no friends and everyone treats him like a baby.  If i tell him to do something even simple like brush his teeth we have a major arguement he just says no.  If i ask him he starts arguing with me and says no im not doing it and it ends up a battle and then me shouting at him and him crying and 20 minutes later him then brushing his teeth and apologiseing.  If i ask him to eat his dinner he says no im not eating at the table i want to eat in the living room so that he can watch TV.  I give him a choice and say you either eat it in the Kitchen at the table or you go hungry simple.  He then starts arguing with me saying no im eating here in the living room and thats it! This carries on and I end up shoutinga nd feeling absoutely drained and gulity for shouting.  It seems that he does this for everything and I dont know what to do.  It breaks my heart that he talks to me in a horrible tone of voice and then lies and says you said the other day that I could do whatever it is that he wants to do.  You are horrible you are nasty to me.  You never listen is what I get from him.  When he calms down I ask him about his behaviour he then apologises and then the next day it starts again.  I have punoshed him by grounding him and not letting him watch TV etc which he then says yes mummy I know Im grounded today and he complies to the punishment.  I think im just frustrated any help appreciated!