Telkom wrongfully debiting my account

I took out a contract with telkom in February 2015,and I pay via debit order. it happened that in May I paid In cash as telkom's system were down. Now telkom is forever debiting my account on the 11th November 2015 they took R1000, and on the 19th November 2015 I paid R1600, 28th November 2015 they debited again. I called them to try and resolve this matter but they are so unhelpful. I'm tired of this people please help.