Oh that's very unacceptable. If you contracted for Naturale and he switched the product, then he has breached your contract with him and you owe him nothing in most jurisdictions until he provides the product and services that are in the contract.

There is no problem applying Naturale over Mega, however the end result may not be the look of untreated wood that you were expecting. The three coats of Mega and the one coat of sealer probably now fills in most of the open graining in the wood. Whether that would overly-compromise the look of just Naturale on the wood is the question you need to answer for yourself.

You could, of course, be somewhat reasonable and agree to allow him to apply the Naturale over what he has already done...only with the stipulation that if the end result is unacceptable, then he would be required to start over. However, Naturale is an expensive product...TWICE the price over Mega, so his 'profit' on the job would begin to diminish, but that is his problem, not yours.

If this was an intentional switch of product and not a misunderstanding or mistake, then you really have more of an issue here.

I wish you the best of luck.

While i agree it is unacceptable your contractor did this a couple of things to keep in mind.

Mega is a Two compont finish. Whether or not they added the hardner is a different question.
Did you physically witness them pour mega onto your floor or did you just see bottles in their truck? While it seems trivial but in a court room
Just seeing a different product in their truck doesnt prove anything.

Also Mega is one of the lighter tones in Bonas product line. I understand it isnt what you asked for but the difference wont be as big as say oil vs water.

You may be okay with how it looks in which case you need to get the price reduced to reflect the amount they charged for specifically The bona product you wanted.

Yes you could add that last coat of the product you wanted but they only thing that would do is change the sheen. Color wise the "damage" is done.

Was there a particular reason you wanted the Naturale? Was it just the color?

Oh, my, Bona finish by a bone head. What ever you do, chronicle your observations in writing and get him to sign that he put on Mega instead of Naturale. Get a picture of the open Mega finish cans if you can.

I would wait to call Bona on Monday and ask for the technical department and see what they say on your question.

Been down this road...