Again a Better responce from EE who seem to have identified the issue and provided a solution:-
I've spoken to EE again and I think this is something people are experiencing who use IPhones
spoke to a helpful lady who said she's had the same issue. Go to Settings - Messages - Send & Receive. ensure that the phone number is the only thing ticked and not the email address
go in to your messages and delete the texts so it doesnt try and default back.
It seems that on an IPhone when it makes an iMessage it is interpreted as an MMS so I have done what EE Technical support has advised as BT Technical support were not interested and will see if this solves the issue!
So EE refund the MMS costs and provide a technical solution - BT Customer service and Technical support say go away its your issue have to love BT