Hi Youssef,
Are you trying to use the ROV with a joystick connected? As per this post you likely need to disable joystick input in QGC or disconnect your joystick while you’re trying to use your script-based control, as otherwise the ROV is sent conflicting information from your script and QGC.
It may also be worth trying to use MANUAL mode (instead of STABILISE) to make sure ArduSub is only doing what you’ve asked it to, and only when you’re asking it to do so.