Hello,
as you can see at
http://www.ofcom.org.uk/telecoms/ioi...istered/s7.xls
Your mobile Number +44 7924 5xxxxx is operated by "Cloud 9" which is a virtual network operator inside the real network of Manx Telecom as I understand the situation.
I'm not sure if all GSM-Networks have instructions how to route Textmessages (SMS) coming or going to this virtual operator.
For example German's virtual network "vistream" has similar problems. +49 157 is given to E-Plus, but vistream uses +49 1570 ... The contract between E-Plus and vistream says, that they have to deal their own interconnection regime for voice calls and Textmessages. vistream customers suffered with disappeared Textmessages. especially with public services which send confirmation SMS to you like railroad companies, Postal services etc. etc.
You could try to open a ticket with travelsim.co.uk maybe they can ask Cloud 9 to solve the solution... hopefully.