Complaining would work, yes, I am not arguing that fact. I strongly support it. I'm saying that most people attempting to occupy phone lines just to cause clutter and chaos would most likely not do so in a way that isn't obviously harassment and would make things worse as it would just be seen as bullying and endanger the livelihood of those just trying to make a living.
The public outcry and fighting back by refusal to use the cards is the underlining point that you mentioned that is what won in the end, nothing else. Boycotting is always the answer. Always. It is the most professional and strong means of obtaining any goal and this is what I have been suggesting to anyone capable of doing so. My bank uses Visa as both credit and bank cards, and I have a large debt I am paying off through them, or trust me, I'd already be refusing to use my card. But that is the main goal here we need to all do as a community; refuse to provide them with an income if possible. They already are taking a large blow financially by refusing to accept payments related to NSFW content, so it would harm them even more and their numbers would drop financially if as many people as possible refused to transfer services using their 'products' (as they word it on their websites when I went to read their policies).
Also, it was nice to see someone who detailed all the things I grew up with lol I was born in the early 80's, and know quite well all the names you dropped and the events. Also, side not about the Discover card is it ultimately failed for a long while because it's policy was no interest, instead charging the company accepting it the interest fees, making most places refuse it. Did not know it was Sears who had created it though. But, I do recall Sears being the K-Mart and Wal-Mart of the 90's. It was the go-to place for everything from professional photography to buying my NES games and school clothes, so that makes sense.
Edit: I'll add Collective Shout is just a patsy. If you look into it, you'll see they are a group of ten people with little to almost no funding until the recent random millions donated to them out of nowhere. MasterCard and Visa have done this many times in the past without any organization pressuring them to do so. Do I despise Collective Shout? Absolutely. But there is no way, in my eyes anyway, that they are the reason two card companies would risk billions of dollars by shutting out the adult industry as a steady source of revenue all for a handful of people. There is definitely a lot more to it than just a few feminazis playing Karen on the interwebs. I don't believe anyone pressured them to attempt to shut down Manga Library Z when they did, for example.