From WhatsApp FAQ:
faq.whatsapp.com
If your account is banned, you'll see the following message when you open WhatsApp: "This account is not allowed to use WhatsApp."
We ban accounts if we believe the account activity violates our
Terms of Service, for example if it involves spam, scams or if it puts WhatsApp users’ safety at risk.
If you think your account was banned by mistake, please
email us or tap
request a review in the app and we'll look into your case. We'll get back to you as soon as we complete our review.
When you request a review in the app, you’ll be prompted to enter a 6-digit registration code sent to you via SMS. Once you’ve entered it, you’ll be able to submit your request for a review and add details to support your case.
We recommend carefully reviewing the
“Acceptable Use of Our Services” section of our Terms of Service to learn more about the appropriate uses of WhatsApp and the activities that violate our Terms of Service.