There can only be two possible reasons for this: first being Kishore's hand is behind the doll and he doesn't want survi to marry tai's son and have her life ruined knowing the kind of person tai is, or tai herself is behind it and she may suspect aniket is playing a double game with her and brought that doll with a camera installed in it to watch aniket and find out the truth. If this second option is true then tai will kidnap her own son just to make sure the wedding doesn't happen. So the doll is either tai or Kishore's doing. I suspect it is Kishore though, as that last shot of him hiding behind the wall in a ghost-like avatar so that pyaare doesn't see him in a previous and recent episode indicated that he is alive and wants revenge.