Email haggler@nytimes.com. Keep it brief and family-friendly, include your hometown and go easy on the caps-lock key. Letters may be edited for clarity and length.

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When interacting with companies on behalf of unhappy consumers, the Haggler encounters endless variations of “We’ll look into this and hope that once we comment, you will go away.” He also gets cold shoulders. Then there are responsive companies that rectify a problem but won’t discuss what caused it, or will discuss it only in ways that suggest that it wasn’t much of a problem.

More like a one-off mix-up. No fixes required. Nothing to learn. We sent a refund, Haggler. Scram.

It’s been a long time since a company candidly discussed a mistake and then honestly engaged with the Haggler about how it planned systemic changes that could prevent others from encountering that mistake again.

That unhappy streak is now over.

Q. When I signed up for Comcast cable service in 2009, I paid a monthly fee to rent a modem from the company. To save money, I returned the modem a year later and purchased my own. A few months ago, I realized that Comcast had, for the last four years, charged about $8 for a modem under “extra services.”