I tried to set a pin for my phone (v720) and now i am locked out

My cousin likes to call people on my phone so i decided that to fix this i would set a pin for my phone.I went through all the steps until it told me to putin my new code. I put it in and then it asked me to re-enter it. When i did it said something along thelines of invalid code.It then asked me to enter my puk code so i did. Then it asked me to put in my new pin and i did it and then it asked me to re-enter it. It then came up with the same as the turn before. I have tried takin the battery out and the sim card but nothing works.
PLEASE HELP