Constant overcharge on contract

I renewed a 2yr contract via Altech Head office continuing on a Straight up 30 Top up with 500MB data per mth the deal included an Apple I phone the monthly cost to be R524.84, BIS was cancelled at time of renewal. In Oct & Nov 14 I logged a complaint for BIS charges *** & 49842 a credit for R2.09 was passed on overcharge of R85.69.Every month my debits have increased to over R600,this month I received a billing of R965.18 I lodged a complaint *** to be told it will take 7 dys to be dealt with. I want a full recon on this account and FULL monies returned vat included to my bank account it is ridiculous that these service suppliers deduct whatever they like from your account this month alone I was overcharged R391.79 other months R79 it is unacceptable as a single working parent don't have time to contact this supplier every month regarding over charges.and they do nothing about it a credit is not acceptable this is theft.