The OP does not get:
-they bought, not the bank
-they could have rented
-they choose the mortgage (amount and term)
-the value of homes will always rise/fall
-the value of a home cannot just be equated to a monetary sum
-negative equity only comes into play if selling
They also don't get that
-their financial future is theirs to make with prudent saving or ruin with excessive spending
-that worrying about negative equity won't get them anywhere
-that despite saying they are not looking for a write off, that is exactly what they asked about.
.