Angry Customer

I have a contract with Telkom and last month when they tried to debit money unfortunately it was finished and they didn't get nothing so because of that they've added R200.00 on my bill just because they didn't find money in my account so I tried calling them to cancel my other contract which is due for cancelation they never pick up the phone when I go to the store I can't get help was told to phone them, so I don't know what do now, I feel that their service is so bad that I ended up not getting helped and my bill is going to get bigger because I won't be able to pay such amount with so much interest that I was not told about when I was taking out this contract phone. Really I'm not happy Telkom