Just hang up, been there, my x racked up bill in the thousands, after our divorce, they really try to scare you. I worked for a collection agency years ago, I know the tactics they use. Saying they will put liens on your property, all kinds of BS they can't do. It's all to scare you.
If, and don't, give them any money you are acknowledging that you are responsible, then they got ya.
Just a little advice,