Yes, you almost certainly do owe them the money. When one business takes over another, it typically takes over the obligations both to and from that business. In your case, it's the "to" that matters--when the second credit union took over the first, they almost certainly took over the book of loans and the accounts payable, which means that any money owed to the 1st credit union will be owed to the second. They can't hold you responsible for amounts accrued because of what one or another credit union did--e..g if there there was a two year period when you couldn't make loan payments because there was no one to pay it to, the interest should probably not have kept accruing for that time--but they can otherwise hold to the amounts you legitimately owe.