I have to say, I just looked into my spam folder a minute ago and there was the dropbox link, sent to me on November, 19, the very same day the dispute at PayPal was opened and resolved.
So I sent again the refunded 11,50 bucks. Then I tried to contact on the webform, but it isn't working.
At this time, I'm a little bit fed up with all these problems to contact Artek Manuals. Since I sent back the payment, I think all is OK now. But I wonder what will happen next time...