Federal law does supercede state law, but liens still do not go away in bankruptcy unless a special motion is filed during the case (called a Motion to Avoid Judicial Lien) to remove them (see 11 USC 522(f)).
So, either you didn't know about the lien during your Chapter 13 (in which case I assume you would have filed the motion), or the lien attached after the case was over.
The lien should not have attached after the case was filed since this is a violation of 11 U.S.C. 362, but sometimes they do.
So, if Discover did inappropriately attach the lien after your bankruptcy, you can tell them they had better remove it since it was a violation of the Bankruptcy Code
If they won't remove it, or if it was on there from before your bankruptcy, then you will probably have to reopen your case and file the motion to get rid of it.
Sorry, wish I had better news. But I guess at least the fact that you can get rid of it, even if you have to jump through some hoops to do it, is good news...
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