Vodacom contracts

Hello! Vodacom is 1 hell of a contract, last year I requested a settlement amount for the purpose of closing/ terminating a contract. I was given the amount that I am supposed to pay and I went straight to Brooklyn to settle the payment. Now I went to open an account I am told that I cannot be assisted because I am owing Vodacom. Ok I called them to inquire about the matter, they telling me that I didn't pay for December as I settled the account in November. My dispute is firstly, I am not working for Vodacom I was never going to be able to pay the amount that I paid unless I asked them, now is it my accountability that the next month was not paid? I am not working at their accounts department and I was never informed about December payment before I requested the settlement. Is it my fault that they didn't include it? ??????