Yeah, Leo FC660C is an awesome keyboard. You should keep it, because it's awesome.
However, to summarize your situation:
1. You ordered a Leo FC660MN with MX Browns.
2. You paid $104 (USD), which is the price of the FC660MN (MX).
3. You received a Leo FC660C (Topre), which has a price of $189 (USD).
4. You got a benefit of $85. And you got somebody else's keyboard.
5. There was some kind of a mistake made, by whom, is not really clear. However, we are dealing with a mistake, and nobody has done anything fraudulent or untoward or with bad intent.
6. You made this mistake public, which is good, I guess, since it shows you are a decent human being who is trying to do the right thing.
7. After trying the FC660C (Topre), you realize that this is the keyboard that you really want. Which is what any sane person would conclude.
8. Now what to do?
ANSWER:
Negotiate a solution with EK Brian. He is a decent human being as well. He does not want to lose $85 on a sale. That is probably in excess of his entire profit for the sale. If you were in USA, he would probably ask that you ship it back. Being in Greece makes shipping it back impracticable, obviously due to the cost and time involved. The best solution is that you pay a little more for what you received. Should you have to pay the full $85? I don't think so. You have had to endure quite a bit of frustration and anxiety over getting somebody else's keyboard by mistake (and it appears that the mistake was not entirely the fault of EK Brian). How much should you pay? I think if you paid $85 less 20%, or $68 (USD), this would be a pretty good solution. But that's my opinion.
In the end the best solution for both the OP and EK Brian is a quiet and amicable resolution to this, out of the public view. That way nobody gets mad at EK Brian for appearing to be a greedy person, and nobody gets mad at the OP for trying to be a DB. Therefore, I think the only practical resolution is for the OP to pay a little more, and keep what he has, and not mention the affair again.