Can you please provide screen recorder for better understanding . Do you have dual sim ? If yes then in which sim do you have problem try swapping sims . Dual 4g is on . If no then check if apn setting are correct , sim bands are supported by device or not . And make sure network selection is on automatic . Try changing network preference . Do your sim show out of service or not available? Sometimes apn ain't set automatically so try searching on google for best apn setting for your network . Check if other company sim work .if yes then reach the company of which it's not working . If no then something is wrong with device only mods and asus can help.