Unfair treatment by Telkom mobile

Last month 25th April telkom debited from my account just before my salary went in so that debit bounced and eventually went through few days later. Then they sent me my monthly statement indicating an additional charge on the next debit as a penalty to the late payment. I tried to explain what happened they totally refused to undo the penalty. In May they wrongly debited me so they owe me, now I tell them charging them the same penalty for taking money from my account with out my authority and agreement. They say no they not gonna pay me they will only reverse the money. My thing is they currently keeping my money, they inconvenienced me with other businesses that i should have done few days ago. Where is fairness?