Ask your Rov.
You should probably pay them the full price for the one they sent you, as you can not return it and it was an obvious mistake, pay them full price for the remanding order, if you still want it and give them a high rating.
They just made a mistake and were upset you took advantage of them.
You probably know in your heart that is the right thing to do. Think of the lesson your children would learn from this!
-1
You took advantage of a price mistake. Ask a rov, check your ethics meter, this is where you have responsibility.
He is selling on Amazon. He has to abide by their rules. Do they have a 'price mistake' clause? If not, he's required to send everything he sold.
He didn't. He lied about what he shipped. He not only didn't send what he got paid for and said he shipped, but he's refusing to send a refund for them!
Being nasty and unprofessional is not against the law or Amazon's T&C.
You can (a) insist he send you the other items you paid for.
(b) You can be nice enough to allow the sale of the unshipped items to be cancelled. He then must send you your refund promptly.
(c)You can go waaay beyond your obligations and return the shipped item, so the seller has no loss (except fees, if any) on this sale.
Since (c) is not your choice, because it's impractical or whatever reason, you need to communicate to the seller what you want from him. It sounds like you want choice (b).
You could point out to the seller that Amazon might back you if you wanted choice (a). Threaten him with going to Amazon to resolve the dispute. See if that shakes your refund loose. But I would (probably check with my Rav then) dispute with Amazon or at minimum give them a bad review.