They are well within time for sueing you. I would ask what they are seeking from you as a primary point and refuse to enter negotiations until they account to you for that figure.(posted 7880 days ago)It looks as if they repossessed the house - you might not have known about this as papers would have been served at the house address - check and find out with the people who are chasing you.
When you have all the facts, you are then in a position to make an informed choice as to your next step - and when you have all the facts, come back to this forum and seek further advice.
An offer in which you raise by lending a sum to offer them might work, and bankruptcy is an option but which may affect any equity you have in your current home. But you need to find out how much is at stake before you make any decision.