If you can't make calls,
- Go to "Settings" on the device > "Data usage" >
at the upper right corner > Turn off "Restrict background data."
If you can't receive calls (but call logs can be seen),
- Go to "Settings" on the device >"Data usage" and scroll down > "Google Services" >Turn off "Restrict background data."
Note: The operation might be different depending on type of device.