Totally unable to bill correctly

I have a Pinnacle 30 Plus Topup contract which I entered into with effect from 30/10/2017. Since then my account has not been correct. At the time, 30/10/2017, I spoke to Ananda to upgrade my previous contract. On 31/10/2017 my account was debited with R139.00, the amount of my previous contract, as it should have been. The new contract kicked in immediately. On 30/11/2017 my account was debited with R45.59 instead of the R29.00. The cost of the new contract. The contract was suddenly cancelled at the end of November. On 7/12/2017 I spoke to Mpho at 1:30. The contract was reinstated. No money had been debited to my account for December. Today I get my statement and it says that I owe R123.07 for December for payment on 31/01/2018. There is no logic in this amount. At the most it should have been R58.00 or less because I was without a contract from 1 - 5 December and I had been overcharged the previous month. This is simply not acceptable.