@Player_busks2ui hello!
From what I understand someone else has taken your in-game Gamertag...now, since it is being "utilized" there's not a, I guess, legal way... What you can do is chat with the other player that as your gamer tag and ask him to change it but besides that there's nothing EA can do... Sorry ☹️
I'm not an EA employee so please, if I helped you in any way press that "Give XP" button, also, if I fixed/solved your problem click "Accept as Solution" please! Thank you!
-SOS Sir.B