Cell C robbing me

I contacted Cell C in Jan as they had double debited my account - they advised it was due to a different deal i was put on - Call ed in Jan - they advise will refund me. then in Feb got a statement for the double amount again - they sd it was due to pro rata fees so the amount the owed me will be taken as well as the installment due, then in march again, today received a statement for double amount and they claim it's pro rata fees again - 2 months in a row to pay pro rata fees?

The call centre don't know what they are talking about, even teh team leaders.

i tried to explain if they had to refund me in Jan that means i was placed on the correct package and paid double in FEB, then now why am i getting a bill to pay double again in March.