MTN Refusing to cancel my contract

I finished my contract back in 2022, and they ignored me when trying to cancel contract, last year 2023 they handover my account to debt collectors because they say I didn't cancel my contract(mind you i contacted retention and always telling me they will cancel my contract but they never did) and i settled the account immediately hoping they will answer my calls for my contract to be cancelled and send me settlement letter.

I paid all the amount last year 2023 and promised me again that they will cancel and send settlement letter. remember the only time they answer the call is when am owing but once paid they ignore until the next owing.

After 3 months now they have started sending me invoices again, meaning they didn't cancel my contract (i was told that it was cancelled).

now back to where we started, fighting and fighting to cancel my contract