As for Misha, I don't like it either when she says bad things against Abhay but I can see where she is coming from because she wants to protect Piya. Since we all know how Piya's nature is extremely curious so Misha is trying to get Piya to hate Abhay so she won't think about him (which obviously is failing). If Misha just said she doesn't know anything about Abhay, Piya would just be even more curious and seriously start investigating about Abhay. So trying to make Piya hate Abhay is Misha's attempt to prevent Piya from finding out about Abhay by simply implying that he is not worth finding out about.
Panchi, on the other hand, I really don't get. She seems totally out of character and I understand she has been hurt in love but I really see no fruitful purpose in dating random guys and then dumping them!