I agree with StevenMax, that you probably plugged in the battery backwards. I've done it too. In my case the battery pack was destroyed by the current and the pins on the RX circuit board were unsoldered, but the servos weren't damaged and the Rx was still usable, just had to plug the battery in to an empty channel. I would inspect the battery pack very carefully before charging it and it it's ok, test it before flying. If you replace the servo, hang onto it, you may need parts later.