This link may be useful to understand the process of Hiring a Third Country National in Austria: https://www.britishinaustria.net/faq/what-is-the-procedure-for-hiring-a-third-country-national-in-austria/ . I would have expected you to have to apply for the Visa-D yourself at your local Austrian Embassy after being given some paperwork from your potential employer. It may be they couldn’t get permission or they found someone who is already entitled to work here. What a crap situation and I don’t think they have been fair to you, but legally I don’t know! We can’t recommend any lawyers but this might give you some English speaking lawyers in Tirol who specialise in Employment law (Arbeitsrecht). The Arbeiterkammer might also be able to offer advice for free. I will also ask the rest of the team if they have any other advice.
https://tirol.arbeiterkammer.at/ueberuns/kontakt/Arbeitsrecht/Arbeitsrecht.html
https://www.tiroler-rak.at/anwaltssuche/?language=3&field=14