recommended actions for the future

setup up 2FA with a PIN and backup email address, this will prevent anyone who acquires your recycled number from reactivating WhatsApp for period of time

recommended actions for now

refer to this page

https://faq.whatsapp.com/general/account-an...-stolen-phones/

email WhatsApp and request account deletion as per the steps under Lost / Stolen, this will take 30 days and will prevent anyone who acquires your recycled number from receiving your pending messages when they reactivate WhatsApp