This is a young worker's problem. After a while, you will learn to ignore the things that are out of your control. After 29 years, I put this kind of crap out of my mind. Does it bother me? Sure. Will I let my mouth run wild, and let it get my BP up and running? Not anymore.
Bottom line: their company, and they make up the rules. Meaning, they can, and WILL, bend, break and change the rules at will. This stuff used to drive me nuts, and I would piss off managers with smart-ass ODS messages, and PCM comments pointing out their hypocrisy. But all that did was put a bulls-eye on my back, and eat me up. After all, if one of us drivers pulled this crap, obviously, we would be fired, post haste for falsifying records and not get our jobs back. I never really cared about having a bulls-eye on my back--I was used to that. What got to me was how much anger I carried around with me.
When you're young, you tend to have an ideal outlook on the world. You think of the world in a zero sum kind of way. You think, "If this is 2/3's empty, then something needs to come along and fill that empty spot." And you think that, maybe, you can assist that process. But experience and hard knocks will correct you're way of thinking.
There is nothing you can do about it. It's out of your control. Now, if one of those customers asked about their package, I would never hesitate to tell them the truth. I would give them the center manager's number and tell the customer to ask him or her what is the status of their stuff. But I wouldn't go out of my way to do so, because you're back in the 'out of your control' area.
Let it go, man. If your managers do this enough, it WILL bite them back. Take comfort in the fact that you are a dumb truck driver. You don't need to think or worry. You just need to show up everyday and collect the big paycheck every week.