“You no longer have xfinity service”

I moved into my apartment and signed up for Xfinity. Initially when I tried setting up my modem I had trouble because the previous renter at my apartment was having a hard time cancelling their internet. Finally Xfinity let them cancel their account, but now when I try to set up my modem it says “you no longer have Xfinity service”. It says I need to make a payment but my balance is $0 because I haven’t received any service yet???? How can I fix this and get internet service ASAP