Charged after cancellation and collection

around Oct of last year i spoke with a rep about cancelling my order as I have moved and no longer needed service i already have sent the gateway back to Xfinity through UPS and was told "not to worry and that everything would be taken care of and all charges would be sent back to my account and i was told a Rep would be calling me soon so i ended the conversation.

a few months later a Xfinity rep called me asking why I had ended my plan to which I had explain that i had moved to a place that already has Xfinity WIFI so Xfinity knew I cancelled and sent back my Gateway months ago and even the app says I'm no longer a active customer but recently I got a notification on my phone saying was sending my "debt" to collections with Eastern Account Systems of Connecticut and i seems im still getting charged monthly despite having no gateway or internet and already stating that i wanted to cancel my service.

I had no problems with this company for the time i was with them until now.

Can someone help me resolve this,