Overcharge

I phoned in july to put both my 2 new data contracts on a 0 spend limit. In spetember my account got deducted with over R700.00 and i phoned the call centre just to find that they never change my spend limit so once again i set the spend limit again to 0 just to find my account got deducted with R955.50 times more then what im supposed to pay(R350.00). I want to cancel my contract bcoz the service is very poor.this is unaccepatable and a *******!!!!! Please sort out this query telkom and get competent staff that can assist me with my ongoing query!!