CONTRACT PAID IN FULL BEFORE ENDING DATE THEN CELL C DECIDE TO CHARGE ME FOR NOTHING

I'm so unhappy and dissatisfied with cell c after I paid my contract in full . Because i overpaid it before contract end now they decide to come to come tell me my contract only end on 13 September that why I need to pay another 415 for what the **** if my fone was paid in full on end of August stop leeching on people and fix your mistakes there ain't no proof where that 415 come from I don't wanna hear your sobby stories u better clear my account and cancel it