Had same issue today on iPhone 12. After update no data and couldnt make/receive calls. Do backup and do factory reset(network reset wont help!!) After downloading backup it should work. Bare in mind for backup recovery you will need to to use your mobile number and if you have only one device you wont be able to receive message for confirmation, so have one spare device just so you can put your sim card in it so you can get confirmation code on that number. As soon as you put confirmation code in iPhone you can put sim card back. Data should be recovered and your cellular should work. Have nice day!