CANCEL INTERNET SERVICE! ASAP!

Hi! I need to cancel my Xfinity Home internet service as soon as possible! I am moving within a day, and tomorrow is the only day I have left with access to a postal service to be able to ship my modem and the rest of my equipment back to Xfinity. I have tried to call the customer service number and the Xfinity agent and nothing has worked so far. Please someone help!