The property in question is a bedroom in a shared 3-bedroom house.
I made the mistake of giving the keys to my not-legally-yet subtenant (n.l.y.s. from here on) and letting him move in, after my landlord acknowledged he had received this month's rent payment from him. After getting some strange answers from the n.l.y.s. when I tried discussing with him the paperwork that needs to be signed, I expressed my concern to my landlord, who sent us both an email explaining to the n.l.y.s. that he is to sublet the room from me, that he is returning payment to the n.l.y.s. (which already happened) and that I'm to present a sublease agreement for him to sign, so that it can all be done properly.
I wrote up a very reasonable sublease, waiving deposit and including some rent prorating, but the n.l.y.s. is ignoring it completely, and won't return any phone calls or text messages. So, on paper, what we have is that the n.l.y.s. has made no net payment, and that I'm still the tenant of the property. But it looks like the n.l.y.s is intending to stay on in the property.
EDIT: he has been in the property for two days (at the time of this edit, 05-07-2017).
EDIT 2: the property is in Atlanta, Georgia.
What can be done in this case?