Why is there no notification for an incoming call?

Question

Android

My mom has a HUAWEI Y5 android phone. At some point, the screen stopped showing notifications of incoming calls. When the screen is off, there are no notifications at all. And if the phone is unlocked, there is a sound of an incoming call, but there is no phone picture to receive a call. What I just didn’t do (rebooted 100 times, cleared the cache, stopped the phone) and what videos I didn’t see enough of, but still I couldn’t do it. So it seems clear what you need to look for in the settings -> "Applications and notifications" -> Phone -> Incoming calls. But I can't move the slider to the right to turn it on. The system does not. When you go beyond the "incoming calls" settings, it generally says: android blocks notifications of this category. Help please How do you end up with a notification? The picture below shows the inactive "Incoming Calls" slider.