2months post cancellation and ISP withholds my line , why?

Honestly there is no service provider that has given me so much grief. I cancelled my account on the 1st of July and it is now the 1st of September 2021, why am I still haunted by SADV? Kindly release my line from your Network so I can move on with my life and stop sending me emails or billing me. The service is pathetic, I cannot get through every time I call. No one responds to my emails.