I'm moving out and hence want to return the rental equipment and end service
You can return your equipment to either a Comcast store or your local UPS store. Either way, make sure you get a receipt and keep it in a safe place for a long period of time. Call Comcast at the number on your bill to tell them you are cancelling service on a specific date because you are moving. Ask them to mail your final bill. Note: if you are in a contract you will be charged early termination fees. This bill is sometimes sent separately from your final bill. Make sure Comcast has your new mailing address and don't forget to put a change of address in with your current Post Office.