Accidentally permanently banned

My friend had my login info and he thought it would be a good idea to mod my service tag, and now im banned from matchmaking. I put my heart and soul into this game in order to get to inheritor including playing for days on end, but all of that will be for nothing if I can’t play on this account anymore! I basically had my account hijacked!

What Can I do?

In the ban FAQ it is specified that even if someone else did the action that resulted in a ban is your fault since it was your responsability to keep the account safe.

Your gamertag and account are your responsibility. If your friend modded/hacked your account, that’s unfortunate however there’s nothing to be done about it.