Have you checked the phone number is correct in the device settings, @Clairec707?

Settings > Phone > My Number 

Yes that's correct too

Maybe the SMS message centre number is incorrect, @Clairec707?

The iD SMS service centre number should be “+447782000800”.

FYI, apparently @Andy Moore solved a similar problem. 

Thabks, where should that be in my settings?

...

having googled this, it is set automatically on an iphone so cannot check it, settings seem to be ok for ID mobile, been speaking to customer services this morning and they have suggested a new SIM which I will collect tomorrow.

got a new sim today, its still not working, Ive just had to repeat the whole story to someone in support, but they have now escalated this issue.

Am at the moment regretting moving to this network :(

If you’re using iD Live Chat, then you’re talking to customer advisers not technical support. 

So just to confirm, you can’t send an SMS text message to any non-iPhone contacts?

correct, yes theyve escalated it to tech support.

But I think I may have just resolved it myself (unless theyve done anything in the background).

I have 2 phone lines, 1 physical ID mobile sim, and another network esim for work.  I thought about trying to turn off my work line and sent a text and it went through.  turned my e sim back on and it still works 

That’s great - which of your SIM / eSIM plans is designated as the PRIMARY line?

ID mobile, its my personal phone so work is mainly just a back up.

https://support.apple.com/en-gb/109317

This Apple online article might be useful.

that was all done, it had been working fine on my previous network, ive only been with ID for a month.  I checked that it was all correct before, I just hadnt tried turning off my esim line before

Thanks though