I also received such letter from "rime" & they called my phone as well. They said if I can faxed them the termination letter, they will not ring / send me letter again. They really keep their promise.
Since the guy from Prime is very polite, I asked them how to chase back the money if the maid go back to Indo / Phil. They said they have partner company there. If the maid go back, they have their own method. But they get problem with by x-yan because my x-yan did not go back to Indo. I think she stay in HK as illegal worker !