One of the lessons here is: never trust a debt collector.
The evidence you cite could be enough to have the judgment vacated, but it is hard to say. You may be able to get the debt collector to voluntarily vacate the judgment, if you can get its lawyers on the phone and provide them with the documentation you have. You may want to consult with a lawyer to assist you on this matter. It would probably not cost much at all and a lawyer may have much more success dealing with the debt collector's lawyer and getting them to act promptly, before this becomes an issue for your credit, etc. If you have any questions, please feel free to contact me at firstname.lastname@example.org.
I also encourage you to visit my Maryland Consumer Debt Defense Blog at www.marylanddebtdefense.com.
Good luck; I am here to help if you need me.
You will file a motion to vacate the judgment, as soon as possible. It is best if you hire a lawyer for a few hours to get this drafted, with the proper exhibits and your affidavit.
If you call the judgment creditor, you may only get a "satisfaction," which will leave a judgment on your credit report and court record.
Don't wait. And if you are in Baltimore CIty, that district court judgment is a lien on real property without filing a circuit court notice of lien.