Original Lender sold my loan to another before going bankrup

[Mike]

Hi-I have a property in Reno, Nevada. I refinanced the loan with my original lender and have all the paperwork to prove it. But somehow this company sold my old loan to another. I've been paying my monthly diligently on the new loan with my original lender but they went bankrupt and now the lender they sold my OLD loan is telling us we owe them. We have all the paperwork to prove that they are holding the old loan. But they stil insist and keep sending collection and foreclosure threats and phone calls. We've forwarded the payments to them (for he new loan) as well as all other payments returned from the old lender but they won't do anything to correct the mistake. What are my legal avenues to correct this?