Vodacom - Running bills and black listing after contract was cancelled00

I cancelled a contract with Vodacom last year which the company duly acknowledged. However, they are still running a balance in arrears, for which I receive no statement and was only brought to my attention when applying for a new contract.

I'm being transferred from department to department and the matter cannot be resolved. Is this really the way to do business Vodacom?! Black list customers without even sending notice of debt ?!