It wasn’t slack, but I’ve had multiple vendors that I was in regular touch with, surprise me with pricing changes in the week(s) leading up to a contract renewal. Never quite this short notice, but definitely as little as 8 business days before the renewal was due.
Both times I’ve paid the new price for 1 year and cancelled. Both times our sales rep was surprised the next year when we didn’t renew.
In this case, it looks like Hack Club sat on a gargantuan bill for at least weeks and maybe months (see top comment on this post).
I'm not denying that what you describe happens, but in this case - ignoring the warning signs, letting the issue crash into a wall and then complaining online about it doesn't help anyone.
I get that regardless there were warning signs, but it honestly seems like slack either miscommunicated or flat out lied to them about the ability to address pricing. While in retrospect they should have started preparing to migrate away, it's human nature to assume good intentions and hope that things will work out well.
There's a couple of interpretations here.
1. The sales rep really thought they would be able to retain good pricing for them and it fell through, and at the last minute hackclub was blindsided by their inability to retain the pricing.
2. The sales rep thought that hackclub was likely to jump ship if they had time to plan based on the new pricing, and lied to them about the possibility of retaining pricing. And thought that by doing so they could force at least one year of higher cost.
3. Hack Club is misrepresenting their communications with Slack to drum up public approval.
My guess is that option 1 is the most likely, and the optimism of the sales rep ended up being a net negative, and human nature being what it is, Hack Club thought things would work out, and everyone is already busy so why borrow trouble.
As for complaining online, sadly it seems that bad press is the only lever that most people have as a forcing factor for companies these days. I honestly only had a Twitter account for a long time, just so I could complain about companies in public to get them to do the right thing, so unfortunately complaining online does actually help.