WhatsApp: What happens to your account when your device gets stolen or lost
WhatsApp only works when the primary device of a user is connected to the internet and is turned on. However, what happens when a user loses their smartphone and are not able to access WhatsApp on any other device.
The first thing that a user should do is lock their SIM card. The user should call their network provider as soon as possible to lock the SIM card. It will then not be possible to verify the account on that phone again, as you must be able to receive SMS or phone calls to verify an account.
After the SIM is locked, the user will have two choices, use a new SIM card with the same number to activate WhatsApp on your new phone. This is the fastest way to deactivate your account on the stolen phone. WhatsApp can only be activated with one phone number on one device at a time.