[benmaraschino]

Not always true. That OOP max often only applies to providers who are considered in-network for your insurance plan. Oftentimes, there's no way to guarantee that all the providers you see during an episode of care will be in-network; you could have a surgery with a surgeon who's in-network, and at a facility that's in-network, but get blindsided by a huge surprise bill from an out-of-network assisting surgeon or nurse or anesthesiologist, or by an out-of-network consult when you're in the ICU recovering after surgery. This is one example: https://www.nytimes.com/2014/09/21/us/drive-by-doctoring-sur...

There's been some progress in states (including CA) to cut down on these sorts of billing practices, thankfully, but it's still a major issue elsewhere, even if you have an ostensibly gold-plated health plan. Many plans are starting to remove caps on out-of-network bills, too: https://khn.org/news/2016-ppo-plans-remove-out-of-network-co...

I assume something similar may have happened to OP, but there are a lot of other ways they can run up the bill. These kinds of billing practices are insane and need to stop.