Cancel my WiFi service out of the country

I need to cancel my Xfinity WiFi service, because I moved out of the country. I cannot cancel over the phone or in person, because I am already outside of the US. I have been trying to cancel online, but I have not been able to. I thought I canceled before I left, but I just got billed. I am unable to get through to an agent online who can help me. 

Could someone please help me cancel my service? I don’t want to keep getting charged.