I got cockatrices as a slayer task, and just keep in mind I'm 1 Defence. I know for cockatrices you should have a mirror shield because their attacks would weaken you every hit otherwise, however I notice without a shield they don't weaken me, and I can't hit on them at all (constant 0s, no matter the attack method.) This leads me to believe that if you don't have a mirror shield on then it's impossible to kill cockatrices? If this is true is it possible to get my task reset?

Correct, there is no check yet to see if the player meets all requirements, hopping online now :)

Update:
There is no check for the defence level in runescape either.

If someone gets this task he can just reset it by talking to the slayer master in burthorpe

-moved to fixed