The best way to solve one of these problems is to be calm, listen to the other side of the story, and come to an agreement that seems fair. If you cannot seem to do this, you need to go get help from the Tournament Desk. If you can specifically ask for the Referee (designated to handle any tournament conflicts) he/she is the one in power. A common mistake in table tennis is mixing up the referee and the umpire. The umpire only controls one match (he/she is the one in the chair watching your match). The referee controls the tournament and has the power to assign an umpire, default a player, and also disqualify a player. Once you report your problem to the referee he will assign an umpire for the match and that umpire will most likely go back to the point in the match/game of where both players agree. Remember, they cannot rule on something they did not see.
Tournaments are supposed to be fun, and competitive at the same time, so try not to let too much controversy get in the way.