Multiple Accounts At Same Address

I have seen a lot of requests across the forums where people wanted two accounts per a single address.   The response has always been the customer needs to have a separate USPS address as the systems will not allow for multiple accounts at Xfinity.   If that is a true statement though why are we getting someone else's bill sent to our address?   We have confirmed there are indeed two accounts for our postal location.  How did this happen when Xfinity representatives have told us their system does not allow it?     Further in trying to speak with Xfinity there is nothing they seem to be able to do about it.   So now we are stuck getting a paper bill from a person who has never lived at this address.