Hi, hopefully I can offer some advice that may or may not be contributing to what is going on.
First things first, you aren't that old my friend -) I have been in the computer field for over 25 years, and I often work with people that are well into their 80's and 90's on the computer. We are only as old as we allow ourselves to be
My first thoughts that come to mind when reading what is going on is that if you are indeed hacked, which is a very loose term, the likely culprit is not likely someone that has found you via the network randomly. When it starts involving access to banking accounts and that sort of thing we must address things like, who else has access to your computer if anyone? What type of email do you use? The most popular ways for people to get information from you i.e. phishing is by sending you emails that look 100% authentic as to where they are from and sending you to clone sites that look nearly identical to PayPal, Bank of America, USPS and more. They offer some reason that you must input your log in information and then they have that information in order to access your real accounts.
People even calling on the phone, offering a call back number to verify they are with the company they say they are from that are also malicious and getting bits and pieces if not all information they need in order to gain access to bank accounts, create credit accounts and more. The world has gone crazy with this dishonest type of behavior.
Without doing a real system assessment I really can't say for sure what is going on, but those are among the most common. These email attachments I mentioned also have what are called trojan horses and more that allow keyloggers, access to web cams and more, there are just to many to mention to be honest.
Having said you have been through 4 machines, have it set to stealth have used every security program etc leads me to think that the email attachments or some other form of phishing tactic is being used.
Please allow me to apologize for any one that has talked to you as a computer technician in a condescending or improper way. This didn't used to the standard way people talked to one another and companies used to know how to treat their customers with respect instead of talking down to them. This is a pet peeve of mine and doesn't happen where I am But to give a reason as to why the Apple gurus and other you have talked to have difficulty understanding is often because they hear the first few words and jump on the possible answers and don't use complete critical thinking skills to think out an entire problem, or they have difficulty understanding what you are attempting to tell them perhaps.
I have listed some of the more common things that cause your type of experiences. They are not necessarily the correct ones but are a good starting point to attempt to track down what is actually happening and chances are they are a number of different things happening at the same time. I hope I have given you some good ideas, and I am completely willing to look into this further with you if you would like the assistance.