Help needed calls don't connect

Hi all. Need help with my galaxy Note3 N900.the phone hasn't been rooted and is running Android 5.0. After a period of inactivity, I can't make or receive calls even though I receive full signal. I have tried the SIM in my LG G2 and the problem is localised to the note. Can someone help please. Once I restart the phone or enable and disable airplane mode, the phone works as normal.

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