You can send first-class mail to the old address with an "Return Service Requested" endorsement. The mail will be returned to you with the new address if the USPS has a forwarding address on file. So you can easily find them for future references and legal if needed. For the rest of the process, go by the agreement, make sure you follow the rules, and everything will work out fine.
UPDATE - Mini G has given me all the statements I need. I have their ID through a verifiable URL path to their Comcast account.
Let me know if I can help you on your case. Hit this to return