Fed up and sick of Cell C

I have been up and down with cell c since i opened my contact with them in June/July 2018. I was in arrears as my previous partner did not pay and contract was on my name, which i ended up taking the phone back and first month i paid an amount short of R2030 to catch up. I then asked to migrate which the consultant told me IT IS NOT POSSIBLE. I struggled to keep up with the payments and in December 2018 i did an EFT for R450 and R968,99 then Cell C still took R824,03 off my account which gives you an full amount of R2243.02. My statement for December 2018 said i need to pay R1417,98 so this means im in credit yet the 31st December they still try and debit me another R448,99. A lady from Cell C phones me today 03-01-2019 as i logged my second call 2 days ago about the debit (first call they were suppose to phone me 24 or 25 December 2018) She says my two EFT payments i did in December 2018 still doesn't reflect on her system after i have sent them proof of payment twice already, sent it for the 3rd time today 03-01-2019. I am so fed up already i want to cancel this contract or just migrate to a lower package but as the Cell C lady told me over the phone again today 03-01-2019 i can't migrate if im in arrears, which im actually in credit!!!! I mean what if i can't affort that amount?