OP
1 Show up everyday at your start time, let them know they can not treat you as if you are on-call.
2 Change your cell phone number and don't ever let management know the new number.
3 Do not answer any calls before your shift in the morning.
3 File a grievance every time they try to work you less than 8 hours.
4 They can't arbitrarily send you back to the Preload... It is called seniority.
5 Let them know that you will file a grievance every time, without exception, that they violate your seniority rights when it comes to pay/hours.
If you do all these things they will start respecting you, and your rights. If you continue to act like their lap dog, they will treat you as such.