MTN Billing for Services Not Received

I have been attempting to cancel bundles on 2 MTN contracts since June this year. And every time I speak to someone, I am assured that these additional bundles for which I am being billed have been cancelled and a credit will be generated to my account. Five months later and with 2 pages of reference numbers I am still being billed for bundles and no credits have been provided by MTN. This is absolutely shocking service and every time I request a confirmation or call back to advise that this request has been complete, no response whatsoever. I would rate their service at a ZERO if the option was available as there is just no service at all.