Debiting incorrect amounts from customers accounts

I cancelled a contract with Telkom within the cooling off period on 12/01/2016. This plan was the wrong plan sold to me on 05/01/2016. I purchased the correct plan and then cancelled the existing one on 12/01/2016 based on the advice given to me by 2 Telkom staff members. I have confirmation from Telkom that the contract was cancelled and all penalties were waived (case number: 1***). This morning Telkom debited my account for R1675.41 which is a pro rata + monthly premium on BOTH devices (BOTH CANCELLED & ACTIVE PLANS). I have the invoice which shows both devices on it. Telkom is currently charging me for a plan that is not active and was cancelled in January. I am willing to honour my active contract with Telkom @ R599pm because that is what I have. I am not willing to pay for a plan that I do NOT have and the device was returned to the store at Telkom's (cancellations department) request. I emailed Bongumusa Si***ane from Telkom, who handled the cancellation but no response from Telkom.