A couple in their early 20s, living in Nashville, subscribed to Comcast home internet service. In their area, that came with a 300 GB data cap. All well and good for these two, since they don’t use much data… except Comcast claimed they did, and billed them for $1500 in overage in less than three months.

The young man’s father wrote to Ars Technica about the bill, and that’s where the saga begins.

Over the course of several months, Ars spoke repeatedly with the customers and Comcast to try to find out what was going on. And while media attention got Comcast to reverse the charges and halt collection on the absurdly high bill, every stone Ars turned over just resulted in more questions about Comcast’s usage meter.

That’s the usage meter that said that two young adults “working long hours” and not home much to use their Comcast connection were using 1,750 GB of data in one month and 2,850 the next — about 5 TB total that the customers insist they never used.

The young couple say they watch a few hours of Netflix a day, but they don’t work at home, don’t run any servers, and don’t really do online gaming.

Netflix HD video can use about 3 GB per hour of data, Ars notes, but you’d have to run it for 33 hours a day in order to hit the usage Comcast claims these customers hit. And as Ars dryly reminds us, days on this planet generally come in the 24-hour variety.

Even while everyone troubleshooted for “leaks,” making sure no-one else was leaching off their WiFi or that no devices had gone rogue, the impossible usage mounted up, like a cartoon dial spinning itself into a frenzy:

One time, Brad was on the phone with Comcast about a notification that he’d reached 90 percent of the data allotment only five days into the month. Minutes later, while talking to a Comcast employee, “I got a message saying I reached 115 percent of my usage,” he said.

Ars reporters sat down to write the story in April, they say — but then it got weird. Because instead of admitting their meter might be faulty, a Comcast spokesperson told Ars that the company was not admitting any fault, and that it stood by its meter readings as completely accurate.

Naturally, Ars asked Comcast to prove it. That kicked off a months-long process of scientific experimentation in the customers’ home, testing one device at a time.

In the end, Comcast said it was their Apple TV that was sucking up all the data. So they sent it back to Apple, who checked it out and found — you guessed it! No issues.

The testing process, though, did indicate that Comcast’s meter was not occupying the same reality as the subscribers’ home. It racked up high usage during a time when nobody was at home to use the internet, and showed low usage during a four-hour stretch when they were actively streaming video.

In the end, nothing got solved. The ludicrous bill went away, thanks to media attention, but neither Comcast nor the customers never did figure out what caused their meter to go nuts… and Comcast never admitted that it did.

This tale of woe is similar to another story from last year, where Comcast told another customer in Tennessee that he’d used 120 GB of data at home — despite being out of the country on vacation. That customer flat-out unplugged his cable modem from the wall for a week, and yet Comcast still told him he used 66 GB of data during that time.

Other customers have complained of the same.

With Comcast’s still-spreading “trial” data cap now going up to 1 TB, from its previous 300 GB limit, at least fewer customers — even those whose data meters are badly on the fritz — are likely to run into overage charges. But if Comcast is going to meter bandwidth at all, it owes it to its customers to make usage meters visible, transparent and, above all, accurate.

Tales from Comcast’s data cap nation: Can the meter be trusted? [Ars Technica]