Whats link multiple msisdns mean

Also, I just checked her messaging activity on the website.  There area hundreds of texts sent to cities all over the country, multiple sent messages per minute, non-stop.  For the three hours that the T-Mobile store was transferring her old data to her new phone, those messages were still being sent, even though her phone line was not even on.  And it's still sending messages from her number, even though she has been asleep in our room for hours and obviously has not been using her phone.    

How can we get rid of this hacker’s access to her phone number?