Angry exclient

I have cancelled my subscription in December 2021. I paid for 2 extra months January and February 2022. Then it was confirmed my subscription is cancelled. In November 2023 I started getting emails from debt collectors for a billing I have no idea came from, I have called the call centre Reference Number: ***8 and they said they will look into this matter. Still nothing has been done. I keep getting emails from debt collectors for something I do not understand and how can my sim be active when I cancelled my subscription in 2021. I am not receiving any of your services. The worse part its more than a year and half later without their services out of nowhere I'm getting debt collectors demanding money I do not owe. Please fix your nonsense