Billed after cancelation of contract

Due to the continuous poor customer service received from Vodacom, I opted to cancel (buy out) my contract with Vodacom and switch to a more reliable service provider. The account in question was prematurely cancelled (Reference number: 520010) by myself on 05 September 2015 at a fee of R 1 321.25 (as invoiced by Vodacom) paid on 04 September 2015. All of the aforementioned was done through Vodacom Mooirivier Mall, Potchefstroom. On the same day I switched to another service provider, keeping the same number. Vodacom however continued to bill me on the same number even though the contract was cancelled, paid up and number not on Vodacom. I was eventually forced to cancel the debit order through my bank as Vodacom simply continued to bill even after me "resolving" the matter with their accounts department on various occasions.

Since then I have been receiving calls from a person identifying herself as Mary from Jacobs Burnard & Associates claiming that I have no other option but to pay Vodacom the monies billed post cancelling my contract and porting my number to a different network. On top of that they claim that I have to pay them a fee for collection. I have even communicated with them via email sending all the proof, with the following response:

Good day,

Thank you for your enquiry via email.

Please be advised client account was cancelled and lines converted to prepaid.

Client last debit order returned unpaid, He is liable for the usage and invoice issued prior to cancellation.

Please continue with collection.

Regards,

Collections: Legal Administrator Mobile: ********** ********** Address: Vodacom Service Park, 1st Floor

The above email would make perfect sence if my account was in arrears prior to cancelling (buying out) the contract. The monies that they are claiming was billed 2 months after cancelling the contract.

I have probably explained this on the telephone and email mare than 20 times, yet to date this matter remains unresolved. Just this morning I received a telephone call from Mary, stating that I have been blacklisted and I must pay...no other option.