Terrible customer service at MTN

I've been trying to cancel my contract with MTN and switch to pre-paid since 1st June (contract expired 30th May). Each time I've called the call centre I've waited up to 20 minutes and no-one has helped me. I've submitted 2 requests, one through call centre and one online. Call centre submitted 2nd June (ref ***), no response. Online submitted 1st June (ref ***1) and they responded today with a cancellation agreement document to sign. They don't mention switching to pre-paid and the document states that I need to give 20 more working days notice (in addition to more than three weeks I've already given since submitting my first request). The call centre assured me that there would be no notice period if I switched to pre-paid, so there's no way I can sign that cancellation agreement. This process has left me thinking MTN has no concern for its customers. If I'm forced to wait another month to switch to pre-paid it will have financial implications for me as I'll save money by being on pre-paid. If this isn't resolved immediately I'm going to switch to another mobile operator altogether once the switch to pre-paid is done.