Every time somebody complains about this, one of these two cases apply (we look at the hand history):
You did not have the best hand. Either you do not remember the hand correctly or you do not know the rank of poker hands. Please read the rules.
There were side pots. You may have won the main pot but players with bigger stacks won the side pot(s) with worse hands, because you were not involved in them. Please, read and make sure you understand the rules before playing and definitely before claiming that the game made an error.