One of the things I find interesting about knowledge is that no one (or at least none of the many, many, many philosophers I have read) can define it. So the conversation looks something like:
"How do you know you know
X?"
"I don't know how, I just do"
While it appears we cannot precisely define what knowledge is, how we can know something/anything, or how we can know for sure that we know what we know, there is (at least) one thing about knowledge we can know: in order to know something, it is virtually impossible for it to be incorrect. In other words, you cannot know something that is not true. For example, I cannot know that a triangle has four sides and four angles because that is virtually impossible. (By definition, triangles necessarily have three sides and three angles.)
What the fuck is my point? Heh...
Is there any chance, any chance whatsoever that VXH does not intend to sell your damaged unit to someone else? If so, then you cannot know that and if that is true, then is it obvious that VXH intends to sell your damaged unit to someone else? Is it obvious that they have any unethical intent whatsoever or is that merely one of many potential reasons they want you to return the glass ?
We humans are incredibly efficient and effective at manufacturing an illusion of solidity, resolution, certainty, predictability, and control out of nothing but our thoughts - and that is the single source of virtually all our unnecessary suffering.
Just sayin'...
I hope this gets resolved for you remarkably soon in a way that exceeds your wildest hopes!