Validation?

If it has a complete up to date payment history it could satisfy part of the validation. What did you ask them to provide? An invoice by itself merely says that at one time you borrowed money or bought something. It does not necessarily meat that you still owe it. How old is the statement from the OC also?

my letter to them requested a copy of the original contract, and a complete billing/payment history.

they sent me the bills from 1/05 through 6/05.

I may be out in left field here, but... It's my understanding that without a copy of that original contract or something else bearing your signature on a promise to pay, they've got nothing. Also, what of the payment history of the account?

Validation also consists of assignment contract.

Here is the law as it is written:

Go to this link. It breaks the whole thing down into simple language and refer to a case that requires the payment history to be provided.
http://www.creditinfocenter.com/rebuild/debt_validation.shtml