Apple didn’t send you a message about your stolen or missing iPhone.
Apple doesn’t get involved with lost or stolen devices.
Apple would never use WhatsApp to send you any kind of communication.
If you followed a link in the message, which you should never do, and entered your Apple ID and password you gave it to the bad guys.
They now have your username and password.
The only way to reactivate find my would require you to have the iPhone in your possession.
Also go here:
https://support.apple.com/en-us/102560
Signs that your Apple Account has been compromised
- Apple notifies you (notification or email) about account activity that you don't recognize (for example, if your Apple Account was signed in to on a device that you don't recognize or your password was changed but you didn't change it).
- You receive a two-factor authentication code (either on a trusted device or via text message) that you didn't request.
- You notice unusual activity, such as messages that you didn't send, deleted items that you didn’t delete, account details that you didn't change or don't recognize, trusted devices that you didn't add or don't recognize, or purchase activity that you don't recognize.
- Your password no longer works.
- Your device was locked or placed in Lost Mode by someone other than you.