Telkom is a scavenger

Telkom is *****ing my money. I had a contract with them. Unfortunately one particular month I missed a payment which was R95. The following month they debited my account with R1500, I called and asked why they took so much, the answer was it's because I defaulted the previous month and that was a penalty. The following week same month the debited my account with R2500, I reversed it and I called, they'd since said they will check and revert back to me, until today I'm still waiting. This has been going on for a good 2 years, they debit I reverse. The sad part is I never get hold of them every time I call. Why would I be charged a penalty of R4 000 for skipping one month?