I have been trying to get this problem sorted for some months but so far iD have failed.
I have tried to text two different 5 digit text numbers (one is the BBC sports page number, the other is TfL's bus arrival update number). They just keep spinning and eventually fail.
My Premium setting is on and set at £25 so no issue there. iD keep asking me to send examples implying they can't think of an explanation at their end. I have done but it does feel that whenever I give examples, the shift the goalposts and ask for info in precise formats.
I notice other people are having similar issues but all iD seem to do is send scripted replies. A friend of mine also on iD is able to message 5 digit numbers, so it must be an issue with the company's settings for my account.
I never had this issue with EE so it is NOT my phone, before anyone asks or suggests.