No Clear Idea whats happening!!

I have been calling for the past month to try understand what is happening with my invoice with Telkom Mobile. I cancelled a contract with them upon receiving a defective device within the specified period(OBF). I then went and got the same device at your store and proceeded to continue with the contract, I was assured that the contract (1st one) had been cancelled successfully and that billing would occur as normal for the 2nd one I took out. Upon receiving the invoice I noted that both contracts (Hauwei Samrt Plan 100) are on it and I am being billed for both of them whereas I only have one device in my possession. I have called several times trying to get an answer, got a case number 173 866 431 and still no-one has given me feedback. On the 25th of January I will now be debited more then I should be and be inconvenienced which isn't ideal and places me in a negative situation. Please can this situation be rectified immediately, I am getting fed up of calling about the same thing with no solution.