your time span of 6 years probably is not a mortgage, it is a bank credit, a loan, debt, bank, friend or whatever, smart move on the builders part, written confirmation that he has nothing further to do with your property, no comeback.
Debt is secured on the property, will show if you want to sell, or the 'creditor' wants their money they come to the owner of the property.
(too late for all this now, brain frazzled)