[Garth Tater]

If your original lender can't prove that they still own your debt you are under no obligation to pay them. If you do pay them and at a later date another entity shows up that can actually prove that they own your debt you will have to pay them - regardless of the previous payments you made to the unproven (fraudulent) owner of your debt.

Student loans, mortgages, bookies, it all works the same way. Make sure you are paying the real owner of your debt not just someone that presents themselves as such.

[doug from upland]

Yes, if there was a valid assignment of the debt and required notice, the debt is collectable. But, there may be a statute of limitations problem if the lender just sat on its rights and did not actively try to collect.