Poor service

Cell c keep dissapointing me with their pooor service. I was in arrears with my payment I paid and I sent them proof of payment but they still debited me for the arrears as well as my monthly payment. Ok i called and requested for a calback they requested that i sent the proof of payment again of which i did 2 days went i didnt hear from them i callled they told me that the money was paid into my cell account without my permission I told them I want the money to paid back intoy account where they took it from then they want me to send proof of payment again and my question is they were able to pay the money into my cell account with the proof of payment i sent them now that i need the money to be sent to my account they want proof of payment again. What is that doesnt their system show that i hhave been overcharged. I cant wait for my contract to end such poor service