The Volkswagen Group's CEO apologized Sunday over the software that reported false emissions data for some of the automaker's vehicles. Above, VW Passats are offered for sale at a dealership in Chicago Sept. 18, 2015. Scott Olson/Getty Images

Volkswagen owners are furious, and they're forming a mob in social media to bang on the gates of their once-beloved brand. Once a brand with a cult-like following, Volkswagen diesel owners are turning on the company with equal passion in the wake of assertions that the automaker used software to defeat emissions tests.

Volkswagen has spent years branding its diesel engines as "clean diesel" to erase Americans' memories of the noisy, smoky truck-like diesels of the past. Volkswagen has spent an estimated $164 million on TV ads in the U.S. in 2015, $77 million of which promoting its diesel models, according to measurement firm iSpot TV.

It worked. Buyers chose Volkswagen diesels for their efficiency and for their environmental credentials: the 2009 Jetta TDI was named Green Car of the Year by Green Car Journal. named the 2015 Passat TDI its "Eco-friendly Car of the Year."

Yet now, the backlash is almost as strong. Volkswagen has yet to announce how it plans to remedy the situation, or if it will at all. But owners aren’t waiting to use the #BuyBackMyTDI, #VWGate and #VWCares hashtags to vent their rage. Volkswagen has gone into a social media bunker. It's official account (@VW) hasn’t posted a tweet since Sept. 17, one day before the EPA went public with its accusation.

Even worse, car buyers concerned about the environment and trying to do the right thing are now coming to grips with the reality they've been spewing 40 times the amount of asthma-causing emissions allowed under the Clean Air Act. James McComb, a student in Long Island, New York, listed his 2002 Jetta for $4,500 and has yet to receive a single response, despite the fact that the care has only 91,000 miles on it, passed inspection and has new tires and a reliable transmission, he told MarketWatch.

“Maybe there really is a smear on the brand,” he told the website, adding he invested a $5,645 into the car on top of his purchase. McComb’s car is not among the models included on the EPA recall list.

Volkswagen could be liable for civil penalties of up to $37,500 per car, or $18 billion. Yet the company has said nothing about how it will reimburse customers and has provided no information on how a fix would affect customers’ cars. Stock shares plummeted by more than 20 percent when markets opened after the EPA’s announcement, and economic forecasters suggested the damage could be bad enough to impact the value of the euro.

The most Volkswagen has offered is a personal apology from CEO Martin Winterkorn before his exit from the company was announced Wednesday.

“I personally am deeply sorry that we have broken the trust of our customers and the public,” he said in a statement Sunday. “We will cooperate fully with the responsible agencies with transparency and urgency, to clearly, openly, and completely establish all of the facts of this case ... We at Volkswagen will do everything that must be done in order to re-establish the trust that so many people have placed in us, and we will do everything necessary in order to reverse the damage this has caused.”