charged for 22 photo messages i did not send from my blackberry on EE orange

Hello I have just seen my bill from May for phone activity in April 2014 and it shows 22 photo messages, sent in sets of about 7, to numbers I do not know, how has someone been able to use my number/phone in this way? and has anyone else had this experience? i can find no record of this in the internet from others. And what can i do? how can I a) stop this happening again and 2) persuade Orange it was not me that sent them? any answers welcome thanks

At the very least let Orange know in case it happens again.

But a friend of mine once had a bunch of text messages billed to his account (back when you had to pay for texting or buy a small package). He call Verizon and they checked something and told him they would remove the charges.