i did get my item back from the chest i was level 6 that time, but when i got out from the dungeon my item and xp was gone and goes back to level 1. good for them they haven't experienced that kind of bug or whatever it is.Your items get removed and stored in a chest at the exit of the unknown dungeon. You should be able to go back in the dungeon via the stairs in the sewer and get your items from the chest. I have not experienced or heard of a player's level going back to zero.
i brought the game and finished last march. then i played mod, so maybe that's the problem because its modified game.Are you using a hacked / modified game?
There's a known issue with people using game modifiers to edit their characters having that exact same issue. It stems from an anti-piracy feature in the game.