One of two possibilities (there are others I dare say) that have happened to me:
- Your servo is drawing too much power from the receiver which is stopping the signal getting to the ESC. This used to happen to me when using Savox servos. Test by swapping to a cheap low voltage servo.
- If that doesn't solve the problem it could be that the PCB on your receiver is damaged.
Basically you need to swap out each element in the chain servo, receiver, esc to confirm where the problem lies but it is most likely a receiver issue.