Actually yes their is. These matches are kept on file for review. So a letter to bungie or activision would allow them to review what happened.
Verbal bullying online now is a crime in many western countries.
Even if the bully was in the usa and your in the Uk . If they investigate and find that threats or other abusive language were made from a legal adult to a minor. Then action can be taken.
Borders are no protection.
English
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Oh ok
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Interpol is one such agency that can direct law enforcement in other nations. Their was a good example a few years back. A man was bullying a young girl in canada , he was from the eu . He was arrested and charged their and is now being extradited to canada.