Supersonic Accounts

I have cancelled my Supersonic account 10 January 20023 and yet they still send me outstanding invoices for this time, I even returned their modem via Postnet. I actually restarted a new account earlier this year and all of a sudden then they started sending me those old accounts which was actually from the previous contract that has been cancelled from them. I do have all the prove for that and even a cancellation email from them. Also spoke to a manger months ago who promised this will stop, but now they even suspended my WiFi account while I am up to date.