wrong debits every month

I have upgraded my contract in September and since then I am charged exorbitant amounts. I was supposed to be paying R139 according to the contract but in October 2015, I paid R698 and R511 was returned upon enquiring. In November 2015, I paid R488. upon enquiring on 03/12/2015 I got this case number ***0 with the promise that they will come back to me. I received an invoice that indicates that I will be paying R198 in December month. My question is, 'will I ever pay the correct amount according the contract we agreed on?'. I just wish to come out of this trouble. please help.