It sounds like you've been entangled in a state support agency that operates like a mechanical machine, possibly with a computer making the lien attach to your joint account because information was fed into the database that you did not pay the child support through the state agency, and the only bank account they could find with your name on it was the joint account.

You have to find an intelligent person with the authority to straighten this out. Knowing how agencies can work when they are flying on automatic pilot all the way, it may take you several phone calls before you lay the matter to rest.

First of all, you have to have some proof that you are completely paid up on your child support obligation. Secondly, you have to find out who is reporting you as not paid up. Thirdly, after you get this cleared up, you have to have separate accounts lest it happen again.

You are separated but not divorced. It's hard to see how they could attach your account without a support order issued by the court.