ilse262,
Since you’re still having difficulty completing a Face Time call on your device, we recommend following the steps in the link below.
If you can't make or receive a FaceTime call on your iPhone or iPad - Apple Support
To perform the steps in the article we suggested above, click and open the link, read the subheadings below, and try each step.
1) Check whether a FaceTime feature is available
2) Update your FaceTime settings after you set up a new device
3) Use a fast connection to avoid sound quality issues with FaceTime
We recommend the steps above because they will show you what to do if you can't make or receive a FaceTime call on your iPhone or iPad.
Should the issue continue follow-up with the steps in the section below.
If none of the above reasons apply to you, and you still can't make or receive FaceTime calls, follow these steps:
1. Make sure that your device has a Wi-Fi connection to the internet or a cellular-data connection.
Learn more if you're using router, firewall, or security software that restricts internet access.
2. If you're trying to use FaceTime over cellular, make sure that Use Cellular Data is on for FaceTime. Go to Settings and tap Cellular or tap Mobile Data, then turn on FaceTime. If you're using an iPad, you might see Settings > Cellular Data.
3. Go to Settings > FaceTime and make sure that FaceTime is on.
* If you see "Waiting for Activation," turn FaceTime off and then on again. Learn what to do if you can't activate FaceTime.
* If you don't see the FaceTime setting, make sure that Camera and FaceTime aren't off in Settings > Screen Time > Content & Privacy Restrictions > Allowed Apps.
* Make sure that you have the correct phone number or email address listed.
4 Go to Settings > General > Date & Time and turn on Set Automatically.
5. Restart your device.
6. Update your device to the latest version of iOS or iPadOS.
Also, as for WhatsApp not working as expected on your device, take a look at the link here: If an app on your iPhone or iPad stops responding, closes unexpectedly, or won’t open - Apple Support
1) Close and reopen the app
Force the app to close. Then open the app to see if it works as expected.
2) Restart your device
Restart your iPhone or restart your iPad. Then open the app to see if it works as expected.
3( Check for updates
To see if updates are available for the app, open the App Store, tap your profile icon, then scroll down to see if updates are available. If updates aren't available for the app, update the software on your iPhone or iPad.
4) Delete the app, then redownload it
Delete the app. When you do this, you might lose data that was stored in the app. Then redownload the app. Then check to see if the problem with the app is fixed.
Please let us know the outcome after giving the above steps a try.
Cheers!