There are two things you might try if you already have the latest carrier settings.
First, connect to iTunes and do a restore as that should correct most software issues.
Second, if that does not fix the problem get a new sim and then ask the carrier to reprovision your account if there are still issues.
After that, if the problem still perists consider doing a device firmware update and setting up the phone as New without restoring anything and seeing if the cellular service works properly for voice, SMS and LTE before attempting to restore any data. If it is not possible to use the cellular service properly at that stage, make an appointment at the Genius Bar or at an authorized service provider to have the phone evaluated.
Yeah I have done everything up to going to the genius bar. I am probably going to go there tomorrow but everything else has not worked. The New Sim card worked for two days but I am back to where I started now.
iPhone 6 says searching/no service/no network