If your debt is with a 3rd party (not the origninal you signed the loan agreement/contract/promissory note ie a party that bought the debt from the original or another debt collector) debt collection agency then i would ask them simply for proof of claim. This is what Thomas Anderson does and shows in his book set. Mark Pytellek also shows a letter with many about 13 points , but Thomas Anderson thinks the shorter the better and more likely you are to get a response or no response within 3-7 days. This is classed as acceptance that what you sent is true, then you have won. You should now be able to use that unrebutted affidavit in court with proof you sent it with a Justice of the Peace or Notary (someone recognised in legal matters) witnessed [copy the witnessed letter and include it with the letter to the debt collector/Bank] and they received it ie registered mail receipt. You could send a letter of non-response using the same methods of proof then default then Notice to Terminate Contract as Thomas Anderson has in his 4th book "Taking on the Banks". You also want to stop the debt being sold on of course.

I found this site helpful and it has alot of the letters that i have not checked totally yet. Although it looks very good and should give you the idea.