My sister had a similar experience - she and her husband own a holiday flat in Turkey. In her case, it was someone she knew slightly through work, but not socially. She sent an e-mail to their wok email saying "Just thought you ought to know that a scam artist seems to be trying to use your name - we had a phone message from someone pretending to be you, trying to invite themselves onto a holiday with us,. We assume it was some sort scam - don't now whether they were trying to get details of when our house will be empty, or when the flat will be, we were immediately suspicious because we knew you would never be so rude as to invite yourself to our flat, but we thought you'd want to know that someone is using your name - you may want to let your friends and amil know, in case someone has hacked our address book or something."
(I can't speak to the exact wording, but it was along those lines. It worked)
If they try to contact you again, and if you or your friends have an e-mail address for them, then something like this might be worth trying!