I'm in the same position, got into debt years ago with Natwest, who sold the debt on and ended up with ccj about 11 years ago, from H & L solicitors.
Today my monthly payment has been returned by their bank, so i did research and found they had ceased trading in December, so now i'm clue less, have no paperwork, received no mail regarding debt, i haven't moved, i cannot pay as bank returns payment. What next?