As referred in the Whatsapp FAQ:
In the unfortunate case that your phone gets lost or stolen, we can
help make sure that no one can use your WhatsApp account.
As soon as possible you should call your mobile provider to lock your
SIM card. Then, it will not be possible to verify the account on that
phone again as you need to be able to receive SMS or phone calls to
verify an account.
After you have locked the SIM in your stolen phone, you can use a new
SIM 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
If you are not ready to activate WhatsApp on a new phone with the same
number we can deactivate your account. Email us with your phone number
in the full international format as described here. Please note that
we are not able to help you locate your phone. Remote WhatsApp
deactivation from another device is not possible.
Important: Even with the SIM card locked and phone service disabled,
WhatsApp can be used on Wi-Fi if you do not contact us with an account
More important details about deactivated accounts:
When your account is deactivated, it is not completely deleted. While
your account is deactivated:
Your name is still on your contacts'
Favorites / Select Contact lists.
Your contacts can send you messages,
which will remain in a pending state for up to 30 days.
reactivate your account before it is deleted, you will receive any
pending messages on your new phone and you will still be in all of
your group chats.
If a deactivated account is not re-activated within
30 days, it will be completely deleted.
Note: Since your chat history
is stored on your device, we cannot retrieve your previous messages.