3.5 BTC is pretty big and how lucky that scammers to get it. Scammers will use different tricks just to catch their prey and the sad thing is that you are one of those prey. It is really sad and we felt it and this is one of the disadvantages of crypto, you can't recover it anymore. Even though a lot of similar things happening around but then, many were still investing Bitcoin and ain't give them a big reason to quite. They are learning their past bad experience and that quitting is not a way to get it back.
How sad, another scam victim using Bitcoin. I don't know if this is probably the result of naive people using Bitcoin without enough technical knowledge on how to use it. Sad to say that probably 25% belongs to this kind of people that we called prey from scammers. If they are educated very well they won't fall into this kind of scammers trap.
Always verify the legitimacy before you will download or update your wallet into the next version, or might pretty good if you actually use the official wallet website not the popup message.