Hi Andygeezer,
Thanks for using the forums to get this issue with your mobile texting services looked into, I am sorry if this has been causing some frustration. I would be more than happy to look into this for you.
Can I ask what make and model handset you have please?
Can you use WhatsApp to create the group?
Do the messages have any pictures, thus turning them into an MMS message?
Thanks,
Megan_L