Edit: Forget it! Mystery solved. They had accidently blocked me and didn't realise it.

Has anyone else noticed a problem with texts not getting through using O2? I would have thought that a widespread problem would have been talked about by now.

With at least one of my contacts (but possibly others), I receive texts from them but they do not from me. We are both using iPhones (mine is a 6s) and are both on O2. I have iMessaging disabled, but I don't know about them.

I can send texts OK to another phone which uses EE and is not an iPhone (an Alcatel).