New York City is suing T-Mobile, alleging that the company used a slew of deceptive business practices, violating the city’s consumer protection law “thousands of times” in the process.

According to the city, T-Mobile and its subsidiary Metro, as well as other authorized dealers, “preyed on consumers” through several tactics. After a year-long investigation, the city says it obtained evidence that, in at least 21 instances, T-Mobile and Metro sold used phones to consumers who paid for new ones and regularly overcharged customers.

The suit alleges that some Metro stores sold phones at a discount, then unlawfully added the tax at the pre-discount cost. The city goes on to accuse Metro of charging customers additional fees without their consent.

According to the city, Metro also advertises a 30-day return guarantee on its website, but in the fine print, it says they only offer a seven-day guarantee for in-store purchases. But the phones, according to the city, can only be bought in-store.

“We take these allegations very seriously and are continuing to investigate so we can respond to the City,” a T-Mobile spokesperson said in a statement. “Though we can’t comment on the specific claims at this early stage, what we are seeing alleged here is completely at odds with the integrity of our team and the commitment they have to taking care of our customers every day.”

The city is asking a court to find that T-Mobile used the deceptive practices, and that it should pay financial penalties based on how often it used those practices.