No caller ID

[Natasha3]

How do I block a no caller ID person they are calling me non stop and it says I can't block them as they are using no caller ID

[MI5]

@Natasha3 

In your call settings there should be an option to block unknown callers (or similar wording).

[Cleoriff]

@Natasha3 

These seem to be doing the rounds at the moment.

Just keep blocking the number. You could ask for a number change but this would require a call to O2 Guide: How to find help & contact O2 

Ther are blocking apps on Play or the Apple store but I haven't used any of them so can't vouch for them

[pgn]

With no CLI on the incoming call, there is no number to block. 

@MI5's suggestion is best, if your phone has that feature.

Be careful - sometimes hospitals and GP practices also withhold CLI, you could miss an important call by enabling "block incoming calls that have no CLI".