Question

Send them a certified letter requesting they validate the debt. If you think you paid it, make them prove you still owe it. Here is a sample one for you to go by. I would also pull a copy of my credit report and see where exactly you stand with this debt.

http://www.debtconsolidationcare.com/forums/debtverification-letter.html

How would I go about showing my credit report?
Just using one of the websites online?

www.annualcreditreport.com to pull your free reports from the Big 3

never ever pay these scumbags again just to make it go away..thats what they thrive on..send a debt validation letter..check your credit reports..cease&desist is always nice to..if the debts outta sol in your state, foad letter works great too! but if you have indeed paid this debt-fight these debt buying fools!!

Looking at my credit report it doesn't even show up, would it be listed if I'd paid it already?

how long ago did you pay it?

So looking at the two other credit reports, they show a negitive balance.
One of which is CITI whome shows I paid off "Account legally paid in full for less than full balance. "
The collections agency is trying to get money on behalf of CITI, would the account numbers match up if they were the same account issue? Which they are/should be but I'm unclear on how to read it all.

The account number for credit cards is often changed when it is sold to a Debt Collector, because part of the card number denotes the carrier.

Find your evidence of payment, request it from the bank if you need to. In the meanwhile, send them the Debt validation letter.