Do you have anything saying that $75 a month is ok?
They would file the papers in the court that's near them. And seeing as how you haven't established residency in your new place, you are still in your old jurisdiction.
Your only chance of fighting this, is to say that they have been accepting $75 a month as a payment for the past year, why is it changing? You have already admitted you owe the debt because of the payments you've been making.

