In the absence of Proof of Indebtedness, a debtor may take the position that they are not responsible for the debt. The burden of proof that a debt is owing is on the parting making the claim. The creditor granting the line of credit can produce this proof either before or as part of some legal process to enforce payment of the debt. One would think it less costly to provide this information voluntarily prior to any legal action as its production might avoid legal action all together.
On the other hand, some collection agencies buy write-offs, statute barred accounts, etc. for pennies on the dollar. They then try and collect or settle the larger debt. In many instances, the original creditor only provides electronic data without hard copies of documentation. If this is what happened here, it is possible that there is no proof of debt other than what appears in electronic data form. This is insufficient. Letitbeover must not cave to collection pressure and make the CA produce the evidence.
Tell the collection agency you "dispute" the debt until such time as proof is provided. The SOL may lapse while you are waiting.