I canceld my service over four weeks ago and paid my final bill why am I getting additional bills for future service?

I sold my house, moved, called to canceled my service over four weeks ago and paid my final bill why am I getting additional bills for future service? I didn't have any equipment to return, I used my own equipment.  When I called to cancel it the rep told me oh we already have canceled this account because the Buyers of the property called us before. Did the Xfinity rep I talked to lie to me and not even cancel my service account?  Even the people now living there have their own Xfinity account and are being billed for service at that property. Appears Xfinity is double billing, two customers for the same address! This is a nightmare.