Need help with new iPhone 8 plus can't call or rechieve calls?

Just bought an iphone8 plus by the Apple store and took my prepaid us cellular sim and put it in the internet seems to work and the sim gets picked up but when I try calling it says incorrect number and when someone calls me it says I'm unavailable is there a fix or a way I can fix this or is there something I have to activate first (this is my first iPhone so don't have an account or anything) I made an iCloud email

But do I need to update the software first I honestly don't know what to do or is it the sim?

Hm

Already asked. Take it back.