MTN debiting account after contract ended

My contract ended in June & I went into the MTN store in Selcourt Towers with a letter stating my contracts needs to be cancelled. MTN has now debited my account for the last 3 months & each time it is a different amount!!! This is not a system error and obviously someone is doing this manually. I tried to contact MTN call centers a few times but every time I get through to someone the call drops or there is no answer at all as well with the excuse of 'High call volumes' <br> This is exactly why I didn't take out another contract with you in the 1st place! None of you have any idea whats going on & data is extremely expensive compared to other networks. This is disgusting service from MTN