Arugueing with the customer

Went to spur last night for dinner and ordered a passion fruit and lemonade, when asked if I wanted another one I said no thank you, but changed my mind and said yeah bring me re-fill anyway this re-fill never came, so I left it as I did not really want it, anyway we asked for the bill I was charged for the 2nd one which I never got, and when I proceeded to tell the waiter you charged me twice for one drink he preceded to argue with me that I did have a second when my girlfriend turned around and said no he didn't he continued to argue with us, I eventually asked for the manager and this was rectified but the nature of how this was handled who gives your waiter the right to argue with 2 people, 2 people against 1 who said we only had 1 drink and not 2 this is not acceptable, I know when I have had 1 drink or 2 drinks..