To determine the amount of money you owe to payoff your mortgage, you should request that your lender provides a payoff demand statement, which is also referred to as simply a payoff statement. This document outlines the payment required to satisfy all outstanding obligations under the terms of your mortgage including your principal loan balance, current monthly payment and any past due interest, penalties and late fees.
The amount of money required to payoff your mortgage is based on your current loan balance and your loan terms as specified in your mortgage note. Unless you entered into a shared appreciation program, the amount you owe should not change based on your value property value.
With a shared appreciation program, you receive a loan in exchange for equity in your home but you forgo a portion of any future increase in your property value. You are required repay the shared appreciation loan when you sell your home, refinance your mortgage or decide to pay off the loan.
The amount you owe to pay off the shared appreciation loan depends on your current property value, with the higher the value, the more money you owe. This is the one scenario when the amount of money you owe may change based on your property value.
We should highlight that shared appreciation programs are relatively uncommon. Plus, these programs do not affect the terms of your first mortgage including your monthly payment and loan balance.
The only other explanation for your question is if you pay property taxes and homeowners insurance into an escrow or impound account. In this case your current property value may impact the tax or insurance you owe and you may be required to address a shortage in the account before you can pay off your mortgage in full. These expenses, however, do not directly affect the amount you owe on your mortgage.
In closing, it is highly unusual that your lender indicated that it needed to evaluate your property to determine how much you owe on your mortgage. I recommend that you ask your lender for a clarification and request a payoff statement to understand how your current mortgage balance is determined.
If you cannot resolve the issue with your lender, I recommend that you contact the Consumer Financial Protection Bureau (CFPB) to look into the matter further. I have included contact information for the CFPB below.
Consumer Financial Protection Bureau
Mortgage Payoff : https://www.consumerfinance.gov/ask-cfpb/what-is-a-payoff-amount-is-my-payoff-amount-the-same-as-my-current-balance-en-205/