Phone unresponsive to incoming calls

Hi! I have a Redmi Note 3 Pro running Global ROM 7.1.8.0 and I am facing a very annoying issue with the network. My phone does not alert me when there is an incoming call when the screen is off/ sleep mode. Incoming calls go straight to voice mail. If I touch the phone and leave the screen on, it becomes responsive to incoming calls. I have tried other ROMs, cleaning cache, changing types of network (2G, 3G), tried another SIM card but nothing seems to fix this problem.
Does anyone have an idea of how to fix it?

Thanks!

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