Bad service from Cell C

I have a fix contract with cell C for the amount of R1440.69 and it stipulate in my contract that I only can go R100 over then they will block it. In September 2019 they debit an ammount of R3 297.91. I phone them. They said the fault was on there side they charge me for my data that was suppose to be included in my package. They will credit my account with R700. Why so little? according to me the ammount that must be credited must be R1857.22???? They also tell me Cell C don't do refunds back into my account :( I need to speak to someone mabe the CEO? My reference number is ***