Preliminary results of a New York investigation found that Time Warner Cable gave customers far slower Internet speeds than advertised, resulting in movies freezing, websites loading endlessly and games becoming non-responsive.

The New York Attorney General’s office disclosed the tentative findings in a Wednesday letter that urged Charter Communications (CHTR) to make major service improvements following its recently completed $79 billion acquisition of Time Warner Cable.

Approved in May by the Federal Communications Commission, the deal also included the Bright House Networks and created the world’s second-largest cable TV and Internet provider. Charter is rebranding the companies under the name Spectrum. Time Warner Cable served 29 states, and provided video, high-speed data and voice service to an estimated 16 million customers.

“In short, what we have seen in our investigation so far suggests that Time Warner Cable has earned the miserable reputation it enjoys among consumers,” Tim Wu, senior enforcement counsel for New York Attorney General Eric Schneiderman, wrote to Thomas Rutledge, Charter Communications’ chairman and CEO.

“In advertisement after advertisement, Time Warner Cable promised a ‘blazing fast,’ ‘super-reliable’ Internet connection,” the letter said. “Yet it appears that the company has been failing to take adequate or necessary steps to keep pace with the demand of Time Warner Cable customers.”

Charter said it has made investments in its core infrastructure, enabling the company to offer “high-quality service organization throughout our footprint.”

“As we progress with the integration of Time Warner Cable and Bright House Networks, we will continue to do the same, bringing all TWC and BHN systems all-digital so that Charter can provide its advanced Spectrum products and services, bringing greater value and more consumer friendly policies, such as minimum speeds of 60 mbps, no data caps, no usage based billing, and no modem lease fees to all our customers,” Charter said.

Preliminary results of the New York investigation found that Time Warner at times let connections with key Internet content providers become so congested that large volumes of data were regularly lost or discarded. This translated into degraded performance for customers who used popular on-demand video services, such as Netflix.

“The problems appear to have been particularly acute at primetime, precisely when many customers log on or tune in,” wrote Wu. “In addition, it appears that Time Warner Cable has been advertising its WiFi in ways that defy the technology’s technical capabilities.”

The preliminary findings stem from an investigation Schneiderman’s office launched in October with a letter that asked Time Warner Cable for information about its broadband customers and the service packages for which they subscribed. The letter sought  “substantiation” for the company’s claims that its customers would receive promised Internet speeds, and also requested documents related to subscriber complaints about the broadband service.

Schneiderman staffers subsequently asked New York customers of Time Warner Cable and other major broadband providers to use open-source tools that tested the Internet speeds they received from the companies.

“The results we received from Time Warner Cable customers were abysmal,” Wu wrote. “Not only did Time Warner Cable fail to achieve the speeds its customers were promised and paid for (which Time Warner Cable blamed on the testing method), it generally performed worse in this regard than other New York broadband providers.”

Schneiderman’s office urged Charter Communications to use the corporate takeover as an opportunity “to clean up Time Warner Cable’s act and deliver the quality Internet service New Yorkers deserve and have long been promised.”

Follow USA TODAY reporter Kevin McCoy on Twitter: @kmccoynyc