Incorrect billing of account

I had a problem with incorerect billing after I requested for my account to be migrated to a straight up line and was charged double for a migration fee and was told I would be refunded one payment and after that no one called to to confirm if a refund will be paid or not and after that I was told I would be paying only R200 for my contract since I was on stright up line but to my suprise I was billed an amount of R500 odd rands and that was more than the amount I was paying for my initial contract since than my account was a mess and now I have been listed by Cell C and cant even apply for my home loan. I am dissapointed and dont want anything to do with Cell C and now they want to charge me for cancellation for of R350 even if my contract has expired with them.