This is a perfect example of how a dealer can jerk around a car owner. Did the dealer prove the filter caused the problem? No, he said it did and then refused to do the work under the warranty. Will it get done? Probably after a fight no doubt, and from the way these things usually go, it will be the vehicle owner proving the filter didn't cause the problem, while the van sits unusable. Another option is to spend a lot of money hiring a lawyer to make the dealer prove the filter was bad. The dealer is in the position of power, not the car owner. FTR I seriously doubt the filter was the cause, as do others, will that help? Time will tell. Good luck!
I'd try another dealership and see how that goes.