Because you purchased said plugins as part of your theme, it is the theme authors responsibility to provide you with all relevant updates to bundled plugins. So usually, whenever a theme update is released, it also includes the newest releases of all bundled plugins.
There is absolutely no need to purchase standalone licenses for bundled plugins (and nobody is forcing you to do so), unless you decide that you either want faster access to updates (in order not to have to wait on the theme author), or direct support from the plugin’s author. Otherwise, you simply wait on the theme author to provide you with the update, and as long as your theme is still supported and regularly updated by the theme author, that is usually not a problem at all, but you might have to wait a little longer to receive all required updates.
This has always been standard procedure on Envato and is clearly outlined in the general market regulations that you acknowledged when you created your account. You bought a license for your theme, and NOT for the plugins. The theme author on the other hand, purchased an extended license for those plugins, allowing him/her to include those with the theme, for the sole purpose so that end users like you do NOT have to purchase those plugins.
But everything that comes free in life has limitations, and when it comes to bundled plugins, those limitations are that the relationship between theme author and theme buyer does not extend to the authors of any bundled plugins, and as such, the theme author is your sole point of reference for updates and support regarding bundled plugins. Anything else would be unfair to the authors of said plugins, because the theme author makes recurrent profit with each theme sale, while the plugin author (beyond the one-time revenue from the extended license, which is just 5x the cost of a standard license), does not benefit at all, and therefore does not owe the theme buyer anything (neither direct updates, nor direct support).
If that approach does not work for you as end user, than the only “real” solution is to simply limit your purchases to themes that do NOT include bundled plugins, which are usually cheaper as well. As for refunds, I recommend you read up on the official refund policy here on Envato …
… and file your refund request with Envato …
… although I’m afraid that you don’t have a valid reason to claim a mandatory refund, and can only hope for good will from the author/Envato.