Cancellation request

I need to cancel my xfinity internet service. I've moved internationally and am no longer within the xfinity service area. I have tried to cancel my service and gotten nowhere. I cannot call a toll free US number from my UK phone, xfinity will not call my UK number (despite multiple agents stating that wouldn't be a problem), I cannot cancel through xfinity assistant (despite the website stating that this is possible), I have provided US VOIP numbers to arrange a callback and did not receive one, I had a friend return my equipment to a local store for me and she was told that she could not cancel services on my behalf, I have spoken to several agents on xfinity assistant, no one has been able to connect me to the cancellation team. Getting to my wits end here. I'm still being charged for internet service for an apartment that I haven't lived in for two months, with seemingly no way to cancel. Help.