Author offering no support and not responding to messages on Envato?

Hi we recently purchased a theme from an Author on Envato - the theme is very buggy, and we are trying to get support for it. Unfortunately the Authors support system is broken and there is no way to submit support requests / queries. And they are not responding to messages on their product page.

If we can’t get support for the product, it’s worthless, given it’s stability thus far. What is the best course of action in this event? Many thanks.