Servo Motor Won't Turn
I think the problem is that you are trying to drive a stepper motor with a servo driver.

A stepper motor is turned in small steps by applying momentary voltages to the various windings.  Steppers do not "spin" when energized, but instead turn one small step per energized phase.
Also, steppers do not utilize positional feedback (usually) because the microcontroller is responsible for counting the number of steps to turn the motor to the desired position.

Servo motors, on the other hand, are regular motors which spin when the windings are energized.  The controller uses a positional feedback indicator and some sort of PID algorithm to supply varying amounts of power to the motor's windings, turning/stopping it at the desired position.

Your code looks like it's outputting the steps to rotate a stepper motor, but if you're using a Servo Driver board, it's intended for a different type of motor... so either 1) nothing happens, or 2) white smoke escapes various components rendering them inoperable.

Good luck.