Retrieving WhatsApp conversation

Hi all,

A while ago, let's say fifteen days back I have deleted a very important conversation accidentally. As I was in great need of this important conversation I have tried almost every possible way to retrieve this conversation (except rooting) without any fruits. It did not work.

I don't know it the data is already overwritten but I would like to ask if it is possible to retrieve it and if anyone has some tips? I have almost tried everything but perhaps anyone can provide me another way or manner. I really need the conversation. Should I contact WhatsApp? Can anyone help?

Thanks in advance!