Unknown Caller ID for Contacts.

[James_A]

All my Incoming calls are Unknown, which includes Contacts stored on phone. 

I have caller ID and Spam protection turned on. 
I have reset Phone on numerous occasions, problem still remains.
This problem arose when I changed my Sim card to a new one. Believing the new sim to be faulty I got a new one, to encounter the same Issue.
My number has not changed since I first contracted with O2.

Any suggestions on how to resolve this matter would be appreciated. 

[pgn]

The only way to get this resolved is to engage with O2 - you can either go into an O2 Shop with some photo id and let them help you, or reach out to O2 directly by calling 202 or by using Social Media as described in the link just below this post will work, @Bartosz-88 - good luck!