If you put the phone number in the search engine top right you will get another thread where people are having this same problem.
On 2.1.15 there is a post from Mat H where he has undertaken to investigate the matter with a colleague and an outcome is currently awaited. It is a bit concerning however that since this undertaking he gave a response to another person over the matter to ring the problem in without any mention of his ongoing investigation.
The most annoying bit is VM customer services agent insisting that picture messages have been sent, to the very person who knows full well that they have not. It looks like something to do with installed apps then it gets far too technical for me.
Couldn't have put it better myself. Not heard a thing from them!! Managed to get onto the 'Chat' bit and they just dismissed me, telling me to contact Virgin Mobile dept!!! In the meantime I'm down £4 and dread next months bill!!! Will keep you informed, mate.