Can't ring out or revive call or txt

[Gemma_2]

I'm on pay&go 02. For some reason my phone wont let me ring out or receive call. Or text. Iv true resetting my phone and no joy. I go to settings and put my sim on O2 and it's saying not connected it just keepseems coming up with a triangle shape at top of my screen

 

[hang-the-9]

If you reset your phone already, contact your service provider for help.