First of, please watch your language, as this is a public forum.
Secondly, your issue seems to be more with the author itself, then with the item you purchased. And you seem to be confusing the author with Envato; those are two separate entities. Yes you bought an item on an Envato marketplace, but Envato is only the platform, and the author is the actual seller.
And whenever item support is provided via external system, authors will always moderate comments and are free to moderate those as they seem fit. Every business (small and large) does so and it shouldn’t come as any surprise to you that authors here on Envato are interested in protecting their “brand” and “item” reputation, especially on a medium like Facebook.
Yes, an author is supposed to fix any serious bugs and errors, if those are in fact bugs and not related to styling or customization requests.
In your case, the author even offered you a refund, which you seem to not want to accept, and really, there is nothing more you can expect from any author, because what more can s/he do? The author is willing to refund you fully and cancel your purchase, and you are the one not wanting to accept it.
What else do you want, that an author can give you at this point? You purchased an item, which does not include you having to like the author, or the author being required to like you; no matter whether the item does what it supposed to do, or not. If it doesn’t, the author is supposed to fix it. If the author doesn’t fix it (provided it is an actual bug/error), you can request a refund, but the author already offered one to you, which you are refusing. You do see how you are moving in a circle here, I hope?
Either you use the item and “work” with the author to the extend the author is willing to do, or you accept his refund offer. You don’t have any other options, and neither should you. This is a simple business transaction and you have been offered a way out. If you don’t take it, then please stop complaining (or at least do it with a much more refined language) and move on.