Not happy with upgrade

MTN and MTN Oakfields is refusing to assist and change the upgrade of our phone. We've had endless hassles the past week with the phone which was upgraded on the 6th March. Although they confirmed there is a cooling off period the only solution to the problem is to send the phone in which will result in another 4 week waiting period. We use the phone for work purposes and as it is at the moment the phone is not sending nor receiving emails. It doesn't store any data either, and yes, we've checked the settings. Point is we are not happy with the upgrade and not willing to use a phone for the next two years which will only give us hassles.