Yesterday im updated android oreo 8.1 version, then my mobile data was not working
Did you try restart or soft reset the phone?
To soft reset: Press and hold volume-up and power simultaneously until the phone restarts and release the buttons when 'powered by android' is displayed on the screen.
Facing the same issue, Mobile data not working in my Nokia 6.1 Plus with BSNL SIM. Any solution to fix this.