Subaru Impreza 2.0R Active G3, gear damage?

Hello, I’ve been a silent reader in this forum for some time now and I have a question for myself… About 4 months ago I finally bought a subi… I was very happy with it until a week ago… When I wanted to leave the gas station in the evening, suddenly the first and second gears didn’t go anymore… before there were no funny noises or the like… the corridors just can’t be inserted anymore… the first one no longer and the second one just “violence” … so off to the car dealership… which now would cost the repair 6000 euros and I would have to take 40Â myself… when I called for the warranty, I thought it was my fault, because I had allegedly driven with the four-wheel reduction. However, that is not true at all. I should now take over the removal of the gearbox and the costs of the examiner… My question(s) now to you… 1. What could be defective? 2. Am I right? (After 3000km and nem Kau) fpreis of 850€) 3. How would you proceed? I would be really grateful for your answers, as I am quite desperate..