rewards

on the xbox 360 i’m having trouble with the
credits being sent to my game after redeeming them.

There are no rewards on Xbox 360. Only on Xbox One.

Source.

is there any reason why is not available on 360?

I’m sure there is a reason, maybe several, but don’t expect an official answer from Turn 10. They’ve completely neglected their fans in many areas and this is one of them.