Hello @daeeun,
You have to provide video evidence unfortunately.
Personally I recommend Instant Replay (assuming you have a Geforce GPU) - it is always recording but only saves when you use the combination of keys which is ALT + F10.
Something you may consider in the future, or better still like what @LogRol mentioned which is to use OBS or other third party recording software.
Alternatively of course you can report users in-game, but that is dependent on whether a Game Moderator is available at that time to review it - which hopefully that shall improve over the next coming weeks, as TruckersMP have recruited more Game Moderators recently. But you're morely likely to get it reviewed if you submit it on the website instead.
Hope this helps!
Kind regards,
xTH3xMoDsZx