Canceled months ago but still getting billed and threatened

I have been in a back and forth email with your accounts department constantly threating to hand me over and still BILLING me for a service I had canceled in the begging of JUN, with email proof of cancellation they are still billing me and no one is willing to help resolve the problem, last email was to try to resolve the issue and no responded then all of a sudden I get billed again and then a Threating email comes through "pay urgently else you will be handed over"

This highly unprofessional when there are email trails of the cancellation but my service is still active when i have not been there for months, how is that customer service ???

Please, could someone address and assist me, enough is enough.

Thank you