My brother saved over my game of fallout 4 when he started a new game... i talked to microsoft and there is nothing they can do to help. I have written Bethesda and I'm waiting for a response. Does anyone happen to know of any way to recover my game????

Your save file is forever gone. Unless you made a back-up.

There is nothing Bethesda can do, because the save files on your Xbox are your responsibility, and only people using your Xbox can interact with them.
Even Microsoft cannot magically bring back erased files.

Next time, make duplicate save slots, and don't let other people play your game without supervision.