They did and you let them!

Short of calling the front desk and dead bolting the door shut, it sounds like your kindness was taken advantage of. I'm sure the workers weren't calling it a day after finishing your room at 11:30 or so.

Your first mistake was staying in a Courtyard.

Definitely write a letter saying how you were coerced into letting them in and how they left the room a mess. But other than a few MR points, I doubt anything will become of it.

I sympathize with your flying in/out of Atlanta, I have to reluctantly do it all the time. Great city, horrible airport and airlines.