Telkom is *****ing my money!

I've upgraded my 5gb data contract that was already been out of contract for years to a 10gb for the same monthly payment. On my account a R900 once off amount appeared. There was no device that needs to be paid up or anything outstanding on the previous contact as it was already a month to month. I phoned them, they logged a case, heard nothing, logged another case to fix the account and still not sorted.