Unknown caller ID

[Stupified]

I appreciate that there have been a lot of other posts, but I remain stuck.

I've gone through O2 support, had the CLI presentation facility bolt on added and had a network reset on my phone - still doesn't work.

Any suggestions or do I just leave O2 and try elsewhere??

[pgn]

You seem to have done most of the things that have helped, it can come down to a change of SIM to correct this, best done in an O2 Shop (bring photo ID with you) @Stupified 

Presumably you did reboot your phone after getting the CLI facility bolt-on added?

If you are in contract, there may be early leaving costs associated with your terminating your contract - Guide: Cancelling Your Contract has most of the info. do not stop your Direct Debit until you are sure your last balance payment has been made.  Test your commonly-frequented places with other vendors' PAYG SIMS before jumping ship from O2 though - not all networks have the same coverage everywhere.

If you are on PAYG, then simply port away from O2 to whatever other network you are looking at - any remaining PAYG balance may be lost in that case though.

Good luck!