Hello and thank you for contacting us. This is Dwayne B. and I’m an expert here and looking forward to assisting you today. If at any point any of my answers aren’t clear please don’t hesitate to ask for clarification. Also, I can only answer the questions you specifically ask and based on the facts that you give so please be sure that you ask the questions you want to ask and provide all necessary facts.
First, federal law (the Fair Debt Collection Practices Act) requires that the collection agency "verify the debt" but not that they provide documentation, which is a common misunderstanding. Verification can be as simple as them calling the original creditor on the telephone and asking "Does this person owe this debt?" When the original creditor answers "yes" then the debt has been verified.
There is nothing in the law that automatically requires them to provide any type of written documentation of the debt. Where that would come into play is that if you were sued you would argue that interest didn't begin running until they did provide something to prove you owed the debt and the exact amount. You would want to send them your request for this, in writing, as soon as you could.
If you have not been sued yet they have to go through the lawsuit process before they can get a judgment and often collection agencies can be beaten because they don't have the right paperwork to prove you owe the debt. There is a very good, inexpensive ebook on handling these situations at http://www.lessonsinlaw.com/the-guerrilla-guides-to-the-law/the-guerrilla-guide-to-how-to-fight-a-debt-collection-lawsuit/
That book also discusses the discovery procedures you use to find out whether they have the documents to prove you owe the debt.