The guy may be counting on Janet not even noticing some random extra
expenses, in which case just letting him know that you're onto him
ought to stop him (i.e., cause him to move on to different victims).
Send a note to the address you have with something like "We're on your
case. Mess with Janet's credit one more time and you'll regret it."
signed with a couple of tough-sounding Sicilian names!