What does "Pull the other one" mean in reply to "forgot they used the service"?
INFORMAL•BRITISH
used to express a suspicion that one is being deceived or teased.
"Your boat was sunk by a swordfish? Pull the other one!"
"Pulling your leg" means that someone is deceiving you (either playfully or spitefully).
"Pull the other one" means that someone pulled your leg, and you are telling them that you noticed by informing them that you have another leg that can be pulled.