Step1. Call the at M$ (1-800-4-MY-XBOX).
Step2. Say technical support, the say xbox live.
Step3. When you get a person tell them that people are spamming you nonstop.
Step4. When they say "block communications" tell them you did but then they tell others to spam you.
Step5. They will prob tell you more crap to do, just say the only way is to change your GT but you dont have any money to get MS points.
Step6. They then will ask what you would like to change it too, so say what you want.
Step7. Free GT Change
Also, if the person your with is being retarded and dosent let you change it, hang up and call again!