Screen not appearing as soon as the call is connected.

Hi there,

Whenever there is a call, my phone screen will go blank and unless the caller hangs up, I cannot end the call from my end because the screen does not appear. I have to use the power button to make it come out of the dialer app. I have tried using factory reset but that did not work out. Could anyone take the pains to tell me how to resolve this issue?:D

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