The cost of a re-build is alays a lot higher than the 'value' of a house so wouldn't get side-racked by this red herring.(posted 7857 days ago)You have encountered the common refusal of lenders to supply information about MIGs. See this site, 'Repossession', 'why lenders refuse to supply documents'.
That they lied about the marketing issue is significant. Keep asking for proof that they valued, marketed and sold the property properly and fairly. That is your right. If you encounter discrepancies in their written statements, you might consider asking the Information Commissioner for an 'assessment request' on the grounds that the lender is holding information about you that is inaccurate and not fit for its purpose.
Why? It all adds up to weakening the lender's 'case' against you. It makes their threats all the more shallow and gives your confidence a boost. These lenders thrive on scaring you into submission. The want you to pay up on unproven 'debts' just to get yur life back; I strongly suspect that at least one lender knows how much people are capable of borrowing and asks for this exact sum as 'settlement' of the alleged 'debt'.
How strong are you? If you follow Lee's advice on this site, you may find it stressful in the short term to fight, but beneficial in the long term to make your stand.