"Punishment "

Your rewards would only be taken off you if you break the rules.

most games ban people for quitting early, its their servers so they can do as they please, you pay microsoft to for access to online play, but most if not all third party game servers are hosted and paid for by the dev/publisher and not microsoft which pockets your money.

rocket league is free to play so you don't pay for it anyway.

say you have been disconnected, well, that ruins the game for others so therefore a few minute ban. if you have bad internet where it happens a lot then its on you to sort that issue instead of spoiling others.

if someone is sabotaging a game or being and idiot in game then report and block done. but never quit.

You must have done something to lose your rewards, this punishment has probably taken off your rewards or You did something to your keys but You don't remember

The punishments for leaving multiplayer events improperly (matchmaking bans) are part of Psyonix's Terms and Conditions which you agree to when you play the game:

https://support.rocketleague.com/hc/en-us/articles/1260801946569-What-Are-Matchmaking-Bans-

This is a support forum & not really the place to ask.

Have a look at this achievement guide/walkthrough here
www.xboxachievements.com/.../showthread.php