Bad Service and wrong billing

Good day I have skipped one payment of December but I paid that amount on the 22nd of December 2017 which was R338 Telkom blocked the connection even after I have paid they said it will take 7days which was today and I am left without connection. When I complain on their Twitter page they say I own they R637 which I don't know on how they got to that amount. Even this month they haven't take their money they wI'll bebe saying I own them an interest again. May you please assist on this.

Thank you for your time