i remember having to actually call an ISP to cancel, as there was no online option, so it was one of the rare occasions of getting a human being on the phone almost instantly and it was
"i'm calling to cancel my service"
"why?"
"cancel the service"
"are you moving?"
"cancel the service"
"are you switching to another provider?"
"cancel the service"
"is the bill too high? would lowering the bill change your mind?"
The moving thing worked for me, I just said I'm moving back in with my parents and they have amazing Internet. Like to me that's a checkmate, they can't say anything