Deceased account

My late husband took out a contract with MTN sometime in August 2022. Both devices were delivered in the last week of August. On the 5th of September unfortunately he passed on. I informed MTN immediately through email that i would like for the contracts to be cancelled as the contract holder is late.I was then afforded 2 options, 1 to return the devices or 2 to make a full payment on the devices and keep them once they are converted to prepaid. I chose to keep the phones and made full payment and sent proof of payment. Last week as I am going through my late husband phone, I discovered an MTN invoice for payment due in September. I then make a follow up today (21 August 2023) via telephone and I was kept on the line for exactly 1h30 min transferring my call from one person to the next as I cannot be assisted because the account is not under my name. I took upon myself to visit the branch and only to be told that the contracts were not canceled. What MTN did was bill me on the payment that I made for the devices in October 2022. This was not the agreement. When i enquire for the contracts to be cancelled now i am told of a ridiculous amount of money that needs to be paid per device. Why did MTN require the death certificate and other documents if the contract of a deceased person will not be closed as per my wishes? I have no energy left in me to fight this. Can anyone assist? I have email trails, proof of payment and other documents that were required by MTN. Thank you. ***