Hi @Hel393. Did you have a WhatsApp account on your previous phone? Did you backup the data on it if so? Are you able to send messages without any issues?
Is this with all contacts? Do you have the Notifications turned on? You can find this in Settings > Notifications.
@Hel393: Can you try heading to Settings > Apps > Whatsapp > Notifications > Select a subcategory > Show As Pop-up, and toggle this option off to see if this restores your notifications?