Already happening. Unless they “recast” it for you you’ll run out of a balance to payoff before you run out of months left that you were supposed to pay. So in year 27 you’ll be done.

The recast option would be beneficial in a cash crunch as it will redo the math and figure out the payment that works so you don’t run out principal due before you run out of months left that you should be paying. Effectively lowering your monthly payment due to your prepayments.