Enable Cheats

Hi!! I'm trying to make myself op but if I type it into the console, it says that the player doesn't exist. Which is weird cuz I'm the player and the only one who's been on the server. If I go to the players tab and click ops and add my player name, it doesn't change anything and won't allow cheats. I have already tried restarting the server and restarting Minecraft itself, I don't know what else to try.