Ok.....I think I understand your situation a bit better now.
Yikes...if you paid with MO (the one option I didn't think about), it would be difficult to prove you paid.
So....the original bank that you worked with sold the remaining balance (the last payment they claimed they never rec'd) to a CA and the CA turned around and got a judgment on you? Am I understanding that part right?
In your first post you said you were never served the documents... I'm assuming you meant for the judgment. If that's the case, then you need to call up the courthouse and find out how you were supposedly served (they have to keep record of this) and then check the Michigan state laws and see if you were served properly. You may be able to file a motion to vacate the judgment.
United States Rules of Civil Procedure, Process Serving Laws ? ServeNow.com
Also how old is this debt? When was the date of first delinquency (the first month you rec'd a "late" notation). Need to see if it's possible out of SOL too.
IF by chance you were served properly......and there is absolutely no way you can prove that last payment......you may need to see if you can negotiate with them. Is it only the collection acct that is on your CRs? or is it also the judgment (in public records section of your CR)?
Hoping I have answered some of your questions........even though I think I posted more questions than you.
Let me know and I will be able to give you more advice.