Home Wifi Cancellation

I got a home wifi from MTN in 2024, used it for about 2 months before I started experiencing serious buffering issues. Funny enough my cellphone worked perfectly well on MTN. I called MTN many times to fix the issue but I was always told to reset the modem. This would work for an or so, then back to the buffering horror. It got worse and worse until I decided to request a cancellation in August 2025. I was told to return the modem to the store and that cancellation would be effected once everything was received. Did so on 31st August, received confirmation that cancellation would be processed on 1st September. Which never happened, I called MTN again in October after I received a new invoice and I was told the cancellation will be done. But today I received another invoice, meaning the cancellation has not been processed still. Please cancel this month-to-month contract, I don't need it.