MTN and Biling with upgrade issues

Wow, so I don’t even know where to start. I’ve got two contracts with Mtn,one of them is expired and on a month to month meaning I’m being billed more for it…..after countless calls I’ve failed cancelling,moving it to prepaid temporarily or even moving back to my previous agreement until I can catch up payments. How do I catch up if I’m being billed more and when I get call nothing happens…..makes no sense at all