It seems possible that the prior owner had more than one mortgage.

Was the tax debt that is the subject of the lien incurred paid before or after you purchased the home? Was it paid before or after you purchased the home? If it was incurred before you purchased the home, was it in fact to be paid out of escrow?

At the end of the day, if you cannot get lien holders to dismiss their claims, there's the option of a quiet title action. But if you can get this resolved without the associated expense and delay, I would try to do so before suing.