Instead of going over very old ground, have a look at the thread that was started when BT notified the Talk21 customers about the closure of the email system. Unfortunately because it is so old some of the links no longer work or take you to the relevant pages.
It's old ground because it was all sent out in 2013. If you binned it or thought it was spam doesn't not negate the fact it was sent.
There is no need for proof of acceptance, what ever that may be. They were not changing the Terms and Conditions. They were stopping the service.
If you did not accept it do you think BT or any other company would keep things running along just for you.
I also think you are wrong about "90% of people don't want to hear your problems, and the other 10% are happy you have them". I suspect it is more like 99% don't want to hear about them.
I don't expect BT to continue to run a service escpecially for me now, but I would expect some kind of back up.
Why BT can't follow the website notes saying suspension and then deletion, I have no idea. It would mean you have a chance to retain some custom rather than just p'ssing people off.