The airplane engines are off and park brake is set but the plane still go back like it is on push back.
So, are you saying that pushback works normally, but the truck doesn't move, only the airplane does ?
The problem is that i cant stop the plane even if i start the engines and set full thrust.
This is normal. You cannot control the airplane if you are being pushed, even in real life.
Everytime i request push back the plane wont stop going back.
Are you sure it doesn't stop ? Maybe it's pushing correctly, just the truck doesn't move for some reason, but it will eventually end.
The only way to resolve the problem is to reinstall GSX and the problem appears again after one day.
This of course is not normal, and the only possible explanation is that you or another addon must have changed some setting that resulted in the pushback truck not moving which, according to your report, seems to be what's really happening, and maybe this setting is reset back to the correct value by the installer.
Two settings in the FSX.CFG that *might* have some relationship with visual issues are the Advanced animations flag (which should always be enabled) and the removal of the notoriously dangerous "Poolsize=0" tweak from the FSX.CFG, which will be removed by the installer.