It appears MailChimp has a chat option for support on weekdays for paid users but since this hasn't been used, one would assume the poster is using a free plan - not exactly exemplary practice for handling anything "mission-critial".
FWIW, MC did respond, saying essentially that there is nothing they are willing to do, and that I need to create a new account. I have written them back asking if I will be able to access my old mailing list from my new account (obviously the answer to that is going to be "no" but I want to get it on the record). They have not responded.
Talking in public about the manner in which businesses conduct themselves is a good thing. It benefits businesses with good customer service and hurts those with bad service. More transparency is good for consumers and for businesses alike.
Shit happens from time to time in business and the normal approach is you connect and discuss by whatever SLAs you align to. You don't scream publicly sullying reputations unless you've given resolution a reasonable shot. Waiting less than 1 business day doesn't seem like giving resolution a reasonable shot. If it were my business, I'd fire this poster as a client.
This the kind of apologetics I can't stand. These things happen because businesses knowingly take actions that negatively affect a small percentage of their user base, but they just don't care if the percentage is small enough.
Software businesses enjoy extremely high gross margins, which means they can afford first-rate customer service. "Bad things happen" isn't an excuse.
But here's the deal, and this might be directly aimed at you, since you say you're in the field. As a home-user who works in the industry and with some interest for tech, I generally only get access to the free-tiers of services offered by players working at world-magnitude. Based on my experience with those services I may or may not advertise them to my friends, colleagues, employers. Especially to employers, because there's a good chance that if there's bad-blood between me and the service provider personally, I might be impaired in my professional activity.
This word-of-mouth type of adversiting is crucial to "2.0" companies, that function based on things such as scale, transparency, growth, reach, efficiency. There's also the different type of provider, the "old business" world, with more business-y and less tech-y practices, such as "call us for a quote" deals, "license per year per seat pe server core", etc. Dealing with them often times involves whole departments (legal + technical) with specific training and paid-for support channels.
If you release and roll perpetuum-beta services and software ("2.0" practice), build your brand on word-of-mouth advertising, on try-for-free honeypots for hobbyists (also "2.0"), don't act "old business" if it comes down to support for a puny user and don't push the "well, it was free, what would you expect?" button. The whole deal of your "we are awesome and scale as opposed to <brand that existed for more than 20 years and sucks just because of that>" is the fact that your machinery doesn't do politics and doesn't discriminate between your users based on estimated pocket girth. It's useless if your solution elegantly "scales" to billions of users, if your business can't secure and treat with dignity the first, lonely user.
Which is exactly what MailChimp failed to do, and what makes this an issue worth the treatment the OP has given it.
* Make sure to have a plan B for all service providers that you use for critical services.
* Make sure you have a secondary copy of critical data, and that you store it responsibly in case a provider does something.
That still doesn't excuse not informing the account holder, but given the short time that has passed, it is possible that task has ended up in someone's backlog.
I'd also add one item to your list: Proper monitoring (which is extremely difficult and time-consuming to set up). A plan B is useful if you know that you need to enact it. Here, the third party provider had silently caused an outage, possibly because they consider shadow bans more effective without considering that the same thing that makes them effective makes them extremely damaging when they're handed out incorrectly.
Created an account, verified my email address. Then i sent a test email to the same email I verified my MC account with.
Immediately, MC disabled my account's ability to send emails. My appeal to support was ignored and eventually, the account was deleted - banned.
So basically, if that person was a plumber, and a bath they installed worked perfectly, you'd now think maybe that was a fluke, because their professionality is "borderline questionable" (is that like borderline borderline, or questionably questionable?)
Yet you say you "don't scream publicly sullying reputations" -- so they're not professional, and now they're "screaming", both of which are things you are creating, while they're stating the cold facts, and they just don't happen to be flattering.
That you can be "professional" without being good, at all, just shows how meaningless that word is.