Azure will alert you when you exceed a budget, but it won't disable anything.

Azure MongoDB billing was insanity. I was up to $800 to host a couple of GB that wasn't doing anything.

I'm still not sure what happened, even their support kept saying "it's priced by request units" and I kept saying "How does a handful of queries a day translate to $40 in request units?"

A year later, I think that I had a lot of collections and they seem to charge per-collection, but I'm still not even sure. Thank goodness we moved off of it after only a month or two.