I really feel for you, and hope you see something back from the money you lost…
That said -and I don want to sound harsh- did that stupidly low price really did not ring an alarm bell? I mean - If an price is “too good to be true”, it is most times just that - “too good to be true”. If somone offers something for such a low price, I would get very suspicious. I such cases I rather do a face-to-face transaction and demand to see everything in working order and also the transaction notes+dongle+serial number sheet (and if second handed - the “transfer software” proof from Steinberg).
As said - I really hope you see something of that money back, but I am afraid chances are not that high, sadly enough…