Ahi esta tu error ademas de los AX
void loop()
{
horzVal = analogRead(horzPin); // Read joystick horizontal position
horzVal = map(horzVal, 0, 1023, 0, 179); // Scale reading to suit servo
horzServo.write(8); // Move servo to required position
vertVal = analogRead(vertPin); // Read joystick vertical position
vertVal = map(vertVal, 0, 1023, 0, 179); // Scale reading to suit servo
vertServo.write(9); // Move servo to required position
delay(15); // Give the servos time to settle
horz1Val = analogRead(horzPin); // Read joystick horizontal position
horz1Val = map(horzVal, 0, 1023, 0, 179); // Scale reading to suit servo
horz1Servo.write(10); // Move servo to required position
vert1Val = analogRead(vertPin); // Read joystick vertical position
vert1Val = map(vertVal, 0, 1023, 0, 179); // Scale reading to suit servo
vert1Servo.write(11); // Move servo to required position
delay(15); // Give the servos time to settle
}