“Our meter is perfect,” Comcast rep claims. It isn’t—and mistakes could cost you.

On March 18, Ars ­­received an exasperated e-mail from the father of one very frustrated Comcast customer.

Elliot told us that his son, Brad, had received bills totaling more than $1,500, and Comcast alleged that Brad had been consistently using far more than his 300GB monthly limit. Overage charges of $10 for each additional 50GB were piling up as Comcast’s meter claimed usage totaling multiple terabytes a month. In February, there were $350 worth of charges for 1,750GB of usage above the 300GB limit (about 2TB total). In January, there had been $570 in extra charges for 2,850GB above the 300GB limit (about 3TB total).

No one had any idea why Comcast’s data meter was producing such high readings, but the cable company wasn’t budging on the amount owed. Brad and his girlfriend, Alison, each 23 and living in Nashville, were working long hours and not using the Internet enough to consume terabytes per month, they say. Making just enough money to cover rent and college loans, they canceled their Comcast Internet to prevent more overage charges, and disputed the amount owed.

Read more: ARSTechnica