Try putting your Galaxy A20 in Safe Mode. This puts your phone in a diagnostic mode returning all settings to default. If your phone works (calls & messaging) in safe mode, then it’s possibly an app-related problem.
To get into Safe Mode, press and hold the Power button until the Power off prompt appears on the screen, then release. Touch and hold the Power off icon until the ‘Safe mode’ prompt appears, then release. To confirm, tap Safe mode. The process may take up to 30 seconds to complete.
When rebooting, ‘Safe mode’ appears in lower-left of the unlock/Home screen. With Safe mode enabled, have someone call you or send you a text message to test. To exit Safe Mode, restart your phone.
If Safe Mode fails to yield results, I would suggest getting the Fongo Mobile app. This will give you a free Canadian phone number that you can use for a callback.
Fongo Mobile app