MTN Contract Cancellation

I bought a home Wi-Fi from MTN online in April. The device was delivered 17th of April. I tried to connect for about two weeks but couldn’t establish connection. In that two weeks I’ve called MTN for assistance with connection but the router still didn’t connect to the internet. I returned the router to an MTN store on the 28th of April and I got a reference. On the 2nd of May I called in for cancellation and provided the reference number as requested. Surprisingly I got debited for the router beginning of June. I always had a separate data plan on my primary number with MTN, so when the debit order went off beginning of June it was the bill for the data plan + bill for home router combined as one. I called MTN customer care and explained that I am not in possession of the home Wi-Fi and it was returned to the store and cancellation done but they couldn’t assist as on their system it apparently shows the contract was still active. I reversed the debit order and made a separate payment for the data plan. Few days later my primary number was suspended. I called mtn to explain the situation and they requested that I get Mondo, their service provider to write a letter stating that the contract is currently undergoing cancellation in order to stop the billing. I called Mondo and they said they are not in liberty to write such a letter. As a result, mtn couldn’t assist me with lifting the suspension on my primary number, even though I have paid for the data plan. As I type this, mtn has yet again debited my account on the 1st of July for both the data plan and the home router. I need assistance with completion of the cancellation process for the home router, I cannot continue paying for a service I never benefited from.