No service after trip abroad

Hi

Since returning from abroad my phone shows as searching or no service, occasionally the service kicks in for a while. I have restored the network settings, restored all the settings, done a hard reset, turned it on and off, backed up the phone, restored from back up, wiped the sim, tried my sim in another iphone 4 (which worked), tried another sim in my phone (which didn't work). The fact that the sim didn't work in my phone leads me to believe its a problem with the phone as opposed to the sim card. I have spoken to my provider who have confirmed there are no blocks etc on the number.

Please can someone help me

Thanks 🙂