Sooo I decided to link my iOS mobile Device Account with my FB Acc. Without further Knowledge about it I also did the same Thing with my Bluestacks PC Account, which is Android. Now my iOS Account got resetted and I have to start from the Beginning. Is there any Way to get back to my old Account on my iOS Device or is it gone forever?

You can try reinstalling your game; if you started your account on your current iPhone it might show up

It wouldn't erase your other account, I use the same logins for 3 separate accounts on both android and ios