I don't know how close or far away they are, but maybe a phone call to a rather higher up person telling them you intend to stop by soon, that you'd like to make sure they'll be there so as not to waste a drive.... you'd like to clear up past, present and if they'll be any future dealings between your and their companies. Be tough, firm, but polite. No sense having it sound like you might've instigated this thing or helped fuel the debate. I'm sure the driver will be lying is butt off to save his job with the company.
I just love face to face confrontations. Shake hands when meeting the guy and then loudly state your case and demand what he intends to do about it. If it's a woman shake hands when meeting and then loudly state your case and demand what she intends to do about it. I'm not big or burly, but I'm frickin' loud and get right down to the nitty-gritty and make sure I'm heard throughout the building.
From what you've described, you might walk away from there with a few free deliveries and someone buying you lunch, so go in there hungry.
Don't expect free merchandise or money back. That's not cool. Get an apology, your tummy filled and get a 1/2 gallon bottle of your favorite booze on your next delivery and then go home.