Show my caller ID switching itself off
I have had issues with my iPhone 5 not receiving calls and going straight to voicemail. When trying to dial out I get "call failed". Incoming texts are taking hours to reach me. I've had a replacement sim card from o2 but still having the same problem. Reading over similar issues on the forum people suggest making sure "show my caller ID" is turned on. It have done this and it keeps turning itself back off again. I have tried restoring my iPhone but its made no difference. I constantly need to keep turning the caller ID back on. I've no idea if this is a network or hardware issue. Any advice would be much appreciated.
iPhone 5s, iOS 7.1.2