I bought a game that wont work

That usually happens, if you use a different Microsoft Account email than the one you used when you purchased the game back then.

Try to think back and find out if you used a different email then. Also go to
https://commerce.microsoft.com and check if your purchase shows up there. If not, you probably used a different Microsoft Account email to buy Mass Effect.

You can go to https://support.xbox.com/my-account/microsoft-account/forgot-microsoft-account-solution to try to find the
Microsoft Account you might have used back then.

Hello,

Are you trying to install the game on the xbox 360 or the xbox one? Also are you signed into the account that the game was originally bought on?

Make sure you are on the same account that bought the game. If you are going back through your purchases find that one and take it to cat support as proof you bought it.

Chat support.

Purchase history.

Thanks for contacting us my name is Samy, I am an Xbox Gamer and I will be helping you today.

How are you, mate?
Do you see the transaction in your purchase history?

https://support.xbox.com/en-US/browse/billing/payment-and-purchases