answer:I guess you can write to pretty near anyone and tell them pretty much anything you want. But if you expect to stay in the house, then you’d better pay off on the mortgage. Mortgages are bought and sold all the time in the secondary market. The mortgage you originally contracted for has more than likely been sold by the originator to some other financial / legal entity (perhaps even a different division of the same company that is responsible for “maintenance” of the mortgage, after the “origination” that got it for you in the first place). Beyond that, companies reorganize themselves from time to time, including changing processes and computer systems, any of which may require them to modify account numbers and “mode of business”. But the thing that doesn’t change is: you sending the right amount of money (at minimum) on or before the right day of each month until the mortgage is satisfied. I would recommend not sending any letter, unless it’s to clarify that the account you’re paying into is to satisfy the mortgage contracted for at [date and time] and known to you as [account number] at [financial institution]. You should receive (or should have received) a notification of the change as a normal part of the mortgage holder’s business.