Are clubs allowed to do this?

So me and my friend went clubbing in hongdae yesterday which we had done before but we wanted to hit some new places. We were told free drinks at this one place so my friend and I wanted to go just to get a free drink when we got to the entrance the guy showed us a drink menu and then we told him we were told free drinks he said no only free entry, that’s the only thing he told us. At that point it was a little weird but we decided still to check it out. We enter and it’s pretty dead and after five minutes we decide we want to leave, as we are walking out they physically hold us back (not gently) saying we can’t leave for an hour since we got free entry and points to the time he wrote on our bands which he never mentioned and we fully told him before we entered we were “just gonna check it out”. So we try to push the guy back so we can leave and he threatens to call the cops even though he was being waaay rougher with us. We ending up talking since we got freaked out about the cops being called and he “let us go” after we paid 15,000 won saying how generous he was being because that was only one persons entry fee. Anyways that freaked us out and was our fist bad experience and was wondering how to handle situations like that in the future?