Have you reinstalled whatsapp?
If your contacts' numbers are shown instead of their names, you might need to reset the WhatsApp sync with your contacts. To do so:
Open your phone's Settings, then tap Users & accounts > WhatsApp.
Tap REMOVE ACCOUNT > REMOVE ACCOUNT.
Open WhatsApp, then tap the new chat icon > More options > Refresh.
If the steps above don't work, it's possible that your phone's settings might be preventing WhatsApp from functioning properly. If so, please try the following:
Open your phone's Settings, then tap Apps & notifications > WhatsApp > Permissions. Make sure all permissions are turned on.