Impossible to terminate my contract.

I'm very frustrated with MTN. I had a 2 year contract which expired last month. I'm trying to go down to a month-by-month prepaid option. When I tried to phone the 2 months ago to give my notice in advance to terminate the contract at the 2 year mark, I was told I have to wait until the month before the contract expires. (They are unable to process advanced notice?!?) When I phoned at the end of the month to now give my one month notice, I was told by the call centre that I have to phone after the 5th but before the 13th (when they'll load my next bundle). So if you miss the 8 day gap, toughies you have to wait another month. It seems ********* that they try and trap you after you've dutifully waited for the contract to be completed. I bet you when I phone again next week there will be another bull dust story. Doesn't make me feel inspired to even stay on as a pre-paid customer if this is how they treat you!!