Pretty soon I received a call from a manager and her supervisor, offering me an apology and telling me that, based on the recordings of my interactions with Oxford staff members, there were “opportunities for improvement.”

They said that Mike, the second customer service agent, was correct and that the drug dispensed initially was coded incorrectly by Oxford’s pharmacy benefits manager — another division of UnitedHealthcare — and should have been classified as a higher-cost, Tier 2 drug. They also called my son’s doctor, and he said my son could switch to the tablet version (with the lower co-pay) and I could crush it myself. Or, they said, I could apply for an exemption to the higher co-payment, citing the confusion.

I’m not sure that every consumer gets such a call from supervisors, so I told them that I didn’t want to be treated any differently because I was a reporter. A few days later, my request for an exemption to the higher co-payment was denied. I was given instructions for how I could appeal.

Mary McElrath-Jones, a UnitedHealthcare spokeswoman, said in an email: “Although we strive for perfection when entering hundreds of NDC [drug] codes and testing our system for accuracy, we sometimes find errors like the one you brought to our attention. And just as we have in this instance, we act quickly to resolve the issue and notify our members.”

Mistakes can happen in any industry. But what I still can’t understand is why Montelukast is listed as Tier 1 in the company’s online formulary. Shouldn’t consumers get accurate information if they spend the time to research a drug’s cost? The answer wasn’t exactly encouraging.

“Our online prescription drug list (PDL) — while comprehensive — is not all encompassing for every drug and classification for all manufacturers,” Ms. McElrath-Jones wrote. “It is published twice per year and includes the top 500 most commonly used drugs. It is a great first stop for our members who wish to know if a particular drug is included in our formulary. For a more customized pharmacy tool, Oxford and UnitedHealthcare members can get specific drug pricing” online.

Many consumers aren’t up for this fuss. They either throw up their hands and pay what’s asked or turn to experts like Lorie Gardner, a registered nurse and the chief executive of Healthlink Advocates Inc., a paid service that helps patients navigate the health care system. “It’s a maze, a complete maze trying to figure out which end is up,” Ms. Gardner said. “There are errors everywhere, unfortunately.”