Text/SMS Messages

It seems that my text/SMS reminders are not working for some reason. I created some test appointments for myself, the email reminders are working ok, but not the text/SMS reminders.

Is anyone else in the UK experiencing this?

I've got the text/SMS reminder switched on for each meeting type. I also set up a workflow for confirmation text/SMS messages but that's not working either.

I'd be ever so grateful for any guidance. Thank You :-)