I gave up on that for a similar issue I had.
All of the notices I get from my bank were showing up in Spam. It took months of telling Google they were not Spam before they stopped going into the Spam folder. Then, 6 months later, they started going into the Spam folder again. The whole process repeated. And again.
Finally, I just wrote a filter to send all of those bank notices to a folder of their own. And when I view them, I get a warning that a filter put them there rather than the Spam folder they would normally have gone to.
My guess is some others would constantly identify such eMails as Spam, instead of going to their account and telling the bank to stop sending them.