Infrigment of my rights as a customer

I cancelled my service with Telkom and was informed that I must pay a penalty for R840. After some time they ran a debit order without my consent for R1200 from my bank account in the middle of the month. Since I get paid at the end of the month, the debit order was rejected and I must pay R150 for an debit order which which failed. I want to know why was a charged more than the penalty amount and if Telkom will pay the R150 to my bank because I gave them no permission to ran an debit order for the penalty amount.