Oh boy, this will be tough. This is not unusual when a bunny is being forced to changed to healthier diet. I am so glad that you changed your bunny's diet, The pellets that have other "stuff" in is like junk food for a bunny. You're bunny is going to feel a kid, who used to eat snickers for dinner, is now forced to his spinach. But it really is the best thing for him.
It might be better to go slow in changing the pellets though and mix it. Over a couple of weeks, lessen the portion of the "bad" pellet until it's not mixed in at all. He, of course, will only eat the bad stuff and leave the healthier stuff. But he won't starve himself. I know my bunnies HATED it when it I switched them to a healthier pellet.
Keep offering the greens, Parsley is a great source of fiber. Once he no longer expects that the "bad" stuff he'll begin to really get into the rest of the healthier choices.
Good luck. Stay strong!