Tesla chief executive Elon Musk steps out of a Model X during a launch event in September at the carmaker's factory in Fremont, Calif. (David Paul Morris/Bloomberg)

When Jay Arbetter put down $40,000 in 2013 to reserve Tesla's newest electric showpiece, the Model X, the Dallas financial adviser was told he'd be driving his roomy, battery-powered SUV by the fall of 2014.

Instead, Arbetter has become one of the many Tesla pre-buyers left in the dark about when he'll get the key — and increasingly frustrated at the celebrated automaker's customer service, which he calls "the worst I've ever received of any company."

Since missing its first shipping date in 2013, the Model X has been beset by repeated delays, raising investor ire over the launch of Tesla's first new car since the Model S in 2012. But the Model X's launch has also raised tensions for some in another important crowd: Tesla fans, who paid up early and now feel spurned for supporting the popular carmaker's next big thing.

Tesla's billionaire chief, Elon Musk, has called the Model X "the hardest car to build in the world," and its feature set boasts much of the space-age wizardry Tesla has become famous for: "falcon wing" doors that open up instead of out, lightning-fast acceleration, and an air-filtering "bioweapon defense" mode that Musk said could prove helpful "if there’s ever an apocalyptic scenario of some kind."

[Elon Musk says Tesla’s newest Model X is aimed at an underserved market: women]

But actually getting all that road magic ready for the masses has proven a challenge. Since the SUV's official launch in September, Tesla has delivered only 208 Model Xs to paying customers — a small fraction of the more than 20,000 Model X reservations logged worldwide by September, according to an unofficial tally from a Tesla fan group.

Tesla stock fell about 7 percent on Monday, its biggest one-day decline since August, after the company said it delivered 17,400 cars -- mostly the Model S -- in the last three months of 2015, at the low end of its earlier forecasts.

“Model X deliveries are in line with the very early stages of our Model X production ramp as we prioritize quality above all else,” the company said in a statement Sunday. Production of the Model X sped up by the end of the year to about 238 SUVs a week, compared to only about five a week at its September launch, the company said.

The Model X shares an assembly line with the Model S at Tesla's plant in Fremont, California, but some production slowdowns have started outside the factory. In November, Tesla said it had stopped outsourcing the production of its custom-made Model X seats after problems with its supplier, and would begin building them in-house.

The delays have bolstered criticism that Tesla, one of America's youngest automakers, is not ready for mass-market production.

[Tesla Model S P90D: A normal person drives the ‘best car’ ever made]

But the company has plenty of reasons to make sure cars are rolling off the line not just quickly, but safely. Consumer Reports, which had once given top honors to the Model S, pulled its recommendation from the sedan last year after drivers reported a series of surprising defects. Tesla was praised for its customer service and responsiveness in handling those flaws, and 97 percent of surveyed owners told the ratings giant they would buy the Model S again.

To handle high demand for the X, Tesla has tried out an unorthodox sales tactic: Pushing customers away. In 2014, Musk told analysts, "If somebody comes in who wants to buy the X, we try to convince them to buy the S. So we anti-sell it. We don’t really provide all that much information or details about the car or provide a definitive date on when you can get it."

Arbetter said his frustrations began when he put in his order for a Model X Signature edition in 2013, before its price and full feature list were unveiled, and was told it would arrive in his driveway in the next year. But as delays mounted, Arbetter said he found it impossible to get any responses from Tesla on the car for months — even when its price was finally set, at $132,000.

Arbetter said he called and emailed the company at least 25 times for an update over the years but was routinely bounced between numerous customer-service dead ends. In September, he emailed all of the directors on Tesla's board asking for information.

[Consumer Reports pulls recommendation of the heavily hyped Tesla Model S]

"The company refuses to talk to its customers," he said. "When someone’s been that loyal for 2.5 yrs, you expect more than, 'We're not gonna tell you (anything). Take it or leave it.'" On one call, when asked whether he wanted his money back, he remembers telling the employee, "I didn't wait 2.5 years for my money. I waited 2.5 yrs for my car."

After a reporter asked Tesla about his case last month, Arbetter said he was contacted by the carmaker for the first time since he paid his $40,000 deposit. He said he now receives daily updates on what stage of production his car is in, but still has no delivery date; he was most recently told the company would try to finish it by Dec. 31.

The company, which declined to speak specifically about Arbetter's case, began offering a similar level of updates for customers after its first Signature deliveries began last month. And on forums like the Tesla Motors Club, drivers who say they are canceling their reservation are joined by just as many who say they are happy to wait. Visitors to the Model X's website are told new reservations will have an estimated delivery in "the latter half of 2016."

Arbetter is happy with Tesla's recent responsiveness, but he said he's still leery until he gets the key.