Yep, we had an incident with Mongo cloud where a bug in their synchronization protocols for Mongo Realm resulted in an insane amount of traffic. This was a development cluster with almost no application load somehow pumping around many TB over the course of a few days. The bill was many thousands of dollars. Their support did the right thing. And we actually ended up with some credits because we were having a rough time with bugs in their software. Ultimately, we gave up on Mongo Realm because it was just not working as advertised for us (high CPU usage on the device, lots of bandwidth, we experienced data loss in the managed cloud storage, etc.). But their support team was great.

Their interests is keeping you as a long term customer. So, they will help you if they can. Unexpectedly high bills like that can end the relation in no time. And 10K is not a lot on a yearly basis. That's a few months of normal usage for lots of companies. So, protecting that revenue is worth something to them. That's also worth realizing when you deal with cloud providers: you are spending non trivial amounts of money on their services and support is part of that deal.