There are many ways you can disable WhatsApp from your mobile device. Let's see them below
Sign in using a different device
WhatsApp can only be active on one phone number. If you ask for a duplicate SIM card and insert it into another device, after you confirm your number, the session you just lost should be closed (and therefore access to your conversations on that mobile should be disabled).
If you go to a physical store of your operator, ask there for the cancellation of your previous SIM card (if they let you) and then the duplicate of it. Replacement cards can usually be made immediately at the store, while if you request it by phone, it may take a few days to arrive in the mail.
Delete all data from the phone
Another option available is to remotely delete all data from your phone. To do this, go to a PC and type Find my phone in the browser's address bar. You will get to this screen, where you will have to select your device:Find My Phone’s main interface
Google will then ask you for your account password to verify that you are the rightful owner of your account. You will reach the next screen, where you will have to tap on the option Consider erasing your device:The phone’s remote control options
A panel will be displayed informing you of all the consequences of this action, then, you will have to tap Yes, erase, and let Google do the rest:Button to erase the phone remotely
Contact WhatsApp Support
The last option we recommend is this. The people responsible for the application notify on their website that if you want to deactivate your account, you should write an email to email@example.com with the subject Stolen/lost phone: please deactivate my account. In the message text, you must repeat the subject, as well as indicate your phone in an international format. That is, your phone number preceded by your country code. For example, if you live in Spain and your phone number is 685 441 332, the email should read +34685441332.