Hey Mona,
Welcome to the Three Community! I'm sorry to hear that you're having so much trouble with crashes, and making and receiving calls. The network doesn't cause crashes so this may be an issue with the phone itself. You may wish to check Samsung's online support, and they can assess if the phone needs a repair, or if they can fix this over a call or chat.
The issue with calls may or may not be linked. Are you able to test your Three SIM in any other phone to see if the call issues are only on your S22 Ultra?
JonathanB
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