Prior to a phone number being blocked, it can be flagged or restricted, due to a poor Quality Rating.
Your WhatsApp business account Quality Rating shows the message quality your customers received in past 24 hours. In case you don't know what's your current Quality Rating is, inquire at firstname.lastname@example.org.
Notify, not spammify
There’s a fine line between sending notifications and spamming the user. It may not even be intentional on the company’s side, but users may perceive it differently if they receive multiple notifications in a matter of hours. The best practice is simply: only notify when requested.
When WhatsApp gets signs of bulk messaging, for instance, the chance of blocking a business number is high. WhatsApp blocks two million accounts every month due to automated behavior.