You should return the unit to your friends son and ask him to pay you back the full amount.
From your response, he took it upon himself to seek a different "cheaper" supplier.
Your friends son should contact the aforementioned seller and demand his money back, in full as well.
I do not know who the formal distributor is for HexCode in Germany, but they possibly can be formally entitled/empowered by HexCode as the manufacturer to inform the local (German, in this case) trade-authorities and try to shut this supply-link down that way.
But perhaps HexCode themselves need to take action upon it themselves, I'm not too familiar with German trade-laws.
But don't be fooled, that the company behind that webshop is apparently located in the UK, according to their website.
And I wouldn't be surprised if that ended being a PO-box company that ends up in, you guessed it, China.
So, from your Sweden you can do little else then request the money back from your friends son.
Taking legal action from Sweden to this "German" company is next to impossible as you yourself did not do any business with them.
That is up to your friends son or HexCode themselves, as their copyrights are being infringed.
But that in the end is often a very difficult, quite lengthy and expensive endeavor, with these types of "shady" webshops.
Your focus should be to get your money back.
And, perhaps very black-and-white, that should come from your friends son.
