Not blaming Chesscom, but just wanted to know
If I lost two games to a cheater, why didn't I got double refund?

I played an opponent recently who got banned. I played and lost two games to him, but Chesscom refunded only +8 rating points. Shouldn't it be +16? For I lost to that guy twice??
You lost 4 points in each game

The rating of a game depends on the difference in Elo.
If you're a 1200 and you play against an 800, the number of points you get for winning is going to be very low; conversely, the points lost for losing will be very high. For the other player, the opposite is true, of course.
Looking at the two games against the banned cheater, it can be clearly observed that the cheater's Elo was a bit higher than yours. Thus, the loss for...losing was much lower.
If you, a 1900, were to play against a 1500 who got banned for cheating, then you'd probably get +14 or +15 back for each game.

Over 74,000 were closed last month.
https://www.chess.com/article/view/chesscom-update-december-2024?#FairPlay
I played an opponent recently who got banned. I played and lost two games to him, but Chesscom refunded only +8 rating points. Shouldn't it be +16? For I lost to that guy twice??