Club Alfa RomeoNederland

It's all very disappointing for you.

But to say that the new Alfa Romeos are bad is utter nonsense. First of all, the automatic transmission is a ZF8, which is one of the most reliable automatic transmissions. You're buying a car with 250,000 kms without a warranty and don't know its history, as I gather from your post.
Using the wrong oil in the automatic transmission is a huge mistake. It must have had problems from the time you bought it. Maybe not noticable for you not knowing a lot about Stelvios. If you don't know much about cars, it's wise to buy one with a warranty. I hope JTD can help you.