MTN retentions service a black hole

I signed up for a service in November. I have not been able to use the service at all and when I queried when I could access the service, in-branch (Canal Walk), in January I was told it was via a reseller and they couldn't help me with it. However, I then started receiving invoices and being billed for it. I have been trying to cancel the service and even shared all the details with MTN's retentions email address, but have received no confirmation. I have tried dialling 083 135 as per email instruction from Customer Care and Retentions but cannot select option 4 as instructed as the voice prompt says it's an invalid selection. I am being billed for something I have not used once! Just an awful circular cycle of non-responsive service. Please help cancel this service