I think the interpretation of (due = owed as a debt)
is not correct.
Due = Owed and payable immediately
Please treat Due and owning as a phrase which basically means “defaulter”
due and owing = Account payable but not paid till today (Defaulter).
The subsequent clause "may seek to satisfy it by foreclosing.” which means: he may forfit the right of the mortgagor to redeem his mortgage.