I am in a similar situation but have had conflicting advice online. I defaulted on a mortgage in France and now Credit Limits International are perusing it. Initially i ignored their letters but they managed to get hold of my mobile number so I had to address the situation. They have sent me a letter with next to no information on just saying that I owe tens of thousands of Euros which was the difference it sold for at auction.
I have been told that if they have bought the debt then they have the same rights as the original creditor, so do I just sit it out and wait for a court summons?