This is primarily a public customer forum. Advice can be offered if more details of the previous Xfinity customer at your address is known. A former roommate or family member? Did you purchase/rent the home at the new address?
Why would I be paying for service to get set up when there is a block on the address have the service for 3 days and now I'm responsible for someone else's bill!
If you are renting, or have bought a house, you need to take your lease/mortgage to your nearest Comcast store, along with ID and/or a utility bill, to prove that you are not related to the previous account holder. Accounts are not just by customer but also by address.