Something similar happened to me last week in Rangsit. I visited a teenage student Chinese girl, and when we're about to sleep, a Chinese man entered her apartment and came into her bedroom. Supposedly to assault her.
When he saw me in her bed he turned around and left. She had given him her passcode to the door previously when she needed help with something. She refused to go to the police about it.
I changed her passcode, provided her with some self defense weapons and that's it. The guy apologized to her said he was too drunk.