please help me in recovering my lost contacts on WhatsApp
The contacts would be safe if you have saved them either in your SIM or have backed up them in your Google Account. The main thing is whether you have a chat backup or not. If not, then I don't think there's any way you can get the chat back on your phone. If it is there (assuming that you have not deleted that backup) then you will get a prompt to install it when you are again logging in with your number.
A same instance happened with me and luckily I had a backup in My Drive account.