Servo library unable to control more than 11 servos
It sounds to me like you're exceeding the current limits of your power supply. Add up the current drawn by your servos (and their controller(s), and also the current drawn by your Arduino and any other circuits you have. I bet you'll find that at 12 servos, you go over the current limit of your regulator. You might need a higher current regulator or a second one.