How to unlock a locked interior door?
You're on the outside of the door, and given both the unlock mechanism appears to not be working, and the "credit card" method don't work, here's another option: remove the hinge pins and take the whole door off.

You just need a hammer and a screw driver (or nail punch, or nail, or something similar) and then push the hinge up from the bottom. You'll probably want a second person to help just in case the door falls over while you're working at the hinges.