Breaching the law / CPA

I recently upgraded my contract with MTN by pre-order the new Samsung Galaxy Note 8. After receiving the agreement via email on the 15th of September, I noticed that the contract did not include as many minutes, sms and data as I would need in a month. I then phoned MTN to cancel the upgrade on the 18th of September well within my cooling off period. And that is where the frustration starts. It has now been 2 weeks and 3 hours on the phone and I am still no closer to cancelling the upgrade than I was at the start. Mtn cannot help me because MTN online did the upgrade and MTN online can't help me because they cannot cancel the upgrade. Meanwhile I haven't received my phone and MTN is billing me for the contract that I don't want.