Unsuccessful upgrade

I am very much disappointed in MTN, I tried upgrading my contract in October 2022 and i wasn't aware that im dealing with Rewards company. So the upgrade was unsuccessful but MTN said the upgrade was successful on their side and expects me to pay the new installment. I've tried everything to prove that the upgrade was unsuccessful and didn't receive any device as promised by the Rewards company but MTN was not interested at all. I've tried contacting the Rewards company but failed. MTN stopped all my 2 lines and referred me to Rewards company to sort out my mess as they want to collect their installment.