hahaha i have similar situation before many times.. and hate to say all of them that do this in my case is not chinese , only thing you can do is find them and talk to them face to face talk until everything is clear. if they still not pay up month after month then is time to find another tenant

no easy way.. but the best thing to do is to find them face to face talk straight to the point until they understand what you need them to do as a tenant or else you say you will find another tenant if they still don't pay up.. since you said you have no agreement with them and don't expect them to pay up the past 3 month rental to you cause they obviously cant for obvious reason ( no money or they just not afraid not to pay )

but renting is like this la..sometime will not so lucky get this kind a tenant..