Dish Network Corp. plunged to the lowest level in 25 years after posting third-quarter earnings that fell well below Wall Street’s expectations and reporting steep customer losses.

Dish reported a 26-cent loss per share in the quarter, while analysts were projecting earnings of 6 cents for the provider of mobile service and satellite TV programming. The satellite TV provider has been transitioning to the wireless broadband business, but even on that front, the company disappointed: It lost nearly five times as many mobile customers as analysts had predicted.