Hi @Hala_093, I'm sorry for the late reply to your post. 
I would recommend that you start with removing both SIM cards from your phone and that you insert them both again.
If you still can't connect to the network, please go to Settings > More > Mobile networks > Network operators and search for available networks. Once the search is complete the network that your operator is using will be marked with a small house icon, tap on that and it should register on the network.
If there is no change after you have done the above, try with another SIM card(s) in your phone. If one of your friends, colleagues or family members have the same size SIM card you can always ask them if you borrow theirs for a short while!
Let me know if that helps!
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