I sold rental property with a mortgage and refinanced the mortgage. How do I enter this?

Under Installment Sales Summary I have properties I sold and enter the principal and interest each year, I owned them for more than 5 years.  I didn't receive a payoff on the mortgage when I refinanced this for the borrower, and the new mortgage is in a new name (the borrower's son).  How should I record this so I don't trigger a principal payoff or a sale of property owned less than a year?  The mortgage balance is higher because past-due real estate taxes were added to the principal balance.  Help!