6 months and still paying for a phone we returned a day after we received it!

In September 2019, my wife decided to make use of the online upgrade option on one of her two MTN accounts. I'd like to note that she has been a loyal client since MTN started in South Africa. The selected phone was delivered late September on a Friday. Due to personal reasons, she was not happy with the handset and the very next day, we returned the handset to the MTN Greenstone Mall store. She was advised to call the online services helpdesk on the Monday with the provided reference number so that the contract could be cancelled and she could upgrade to an alternative phone. Today is the 19th of February and to date, the contract has still not been cancelled, and every time we contact MTN, telephonically or in person, we get the same nonsense story. MTN blames a 3rd party who has not completed the return of the phone to allow for the contract to be cancelled, and the 3rd party says that they cannot facilitate the cancellation of the contract as they do not have the agility to do so. Now, maybe I am a total *****, however, I do not understand why it is the customers problem when a so called service provider cannot fulfill the promised service due to the incompetency of a 3rd party. What is worse is, since the upgrade, we have had to pay, every month, the full amount, for a phone we do not own! The last time we spoke to MTN, we advised them that after 5, now 6 months of them charging us for a phone we do not have, we will turn to social media to expose their total incompetence. Guess what happened. Nothing! So, here we are!