It sounds as though you're pretty much doing all you can - remember, they DON'T want to go to court over this. The onus is on them to prove the debt, not on you to prove you don't owe the money.(posted 8292 days ago)If it were to go to court, the judge would look most unfavourably on their tactics to date.
"I have tried to sort this out without wasting the court's time, m'lud, but the mortgage company and their solicitors have been most unco-operative, sending illegible documents, and taking 8 months to supply a SARN. They have, so far, refused to supply a complete breakdown of the alleged debt, so I cannot say how much, if anything, I owe them".
Good luck !