Server saying ??? Can't log in

So on my aternos server, my friends and I accidentally made a command block that created fireballs that spawn from other fireballs, this obviously caused the server to crash. To fix it we restarted the server turned off command blocks and send a /kill @e command through the server page. Then we tried to log on and break the command blocks but next to where it displays your ping it says ???. The ping display doesn't show a red X through it. Any one know what is going on and how to fix it?