Telkom is ripping me off

I am very disappointed in Telkom. Last month they charged me over 200 for a returned debit order. This is madness. It's almost the same as my monthly instalment. My balance was over a 1000. I paid 429 then my balance was 626 which i intended to pay before month end. Now yesterday they tried debitting the 626 which also was returned. Meaning they are going to add the 200 to my bill for the month. I never agreed to them debitting my account on the 15th. I am very angry. If they going to charge that extra 200, i want them to come get their router and cancel my contract. This is a lot!