Someone has hacked my phone account

I recently got a message from MTN saying that my payment details have been updated.<br> Then I got a message from MTN that my details have been updated.<br> Then I get a message from MTN saying that I have successfully upgraded my contract (07/10/2015)<br> Then all my data gets depleted and data is purchased recurringly and then gets depleted.<br> Then I get a message that I have exceeded my usage limit<br> Now I get a message from MTN that the phone is suspended.<br> <br> Oh my word. What is going on here. I have not updated anything. I have not upgraded anything.<br> <br> What is wrong with MTN, how can someone else be using my phone account?<br> <br> Someone callled us trying to seel us a new ****le. He called more than 3 times on behalf of MTN.<br> He has changed our contract. I wish to have him arrested!!!<br> <br> HEEEELLP