In the service's FAQ, the reasons that lead to account suspension are explained. Here's what to do to prevent this from happening
If you use WhatsApp a lot to exchange messages, pictures and videos with your contacts, you are certainly used to considering this app part of your daily experience. If we don't consider the downs of the service, in fact, WhatsApp is always available and you can use it for free without major limitations. Unless your account is suspended.
Account suspension is an event that, for most WhatsApp users, is absolutely rare. When it happens, however, you cannot use the service from any of your devices and you receive the message "Your phone number is suspended from using WhatsApp. Please contact support." The suspension of your WhatsApp account, in fact, is at the level of the phone number and not the device through which you use the application. If your account has been suspended, the reason is almost always your own misbehavior. Even if, perhaps, you did not do it on purpose. If you are looking for the reason why WhatsApp is suspending your account, it is very likely that you will find the answer in the "Acceptable Use of Our Services" section. This section of WhatsApp's terms of service lists everything you can do with the app and, consequently, what you cannot do.
It is acceptable to use WhatsApp in accordance with the law, so it is not okay if you use WhatsApp to violate the privacy of other users, violate copyright law, share content that is "illegal, obscene, defamatory, threatening, intimidating, annoying, undermining, offensive to a race or ethnicity, or promotes or encourages illegal or inappropriate behavior, including promoting violent crime," and so on.
WhatsApp defends itself
In addition to "not hurting" others, WhatsApp also makes sure that you don't hurt WhatsApp itself. Of course, the Facebook Group is looking out for its own interests and one of the possible reasons why they may suspend your account is because you have been using apps that interfere with the legitimate interests of Facebook Inc. The typical case is the use of apps like unofficial versions of WhatsApp or fake apps like WhatsApp Plus and GB WhatsApp.
Keep your account secure
WhatsApp has over a billion users worldwide, which is why it is unthinkable that they can control the security of every single account. The security of your account, therefore, is your responsibility and if someone violates your profile and WhatsApp notices (usually because the violated profile is used to send spam in a massive way) then that account is blocked. WhatsApp, in fact, clearly states that you "must promptly notify us of any unauthorized use or breach of security of your account or our Services.