AT&T was hit with a $224 million lawsuit as a cryptocurrency investor accused the US operator of fraud and gross negligence in relation to the theft of digital currency.

The investor, Michael Terpin, alleged digital currency tokens he owned were stolen from his mobile phone account, for which AT&T is the service provider. In his lawsuit, he described the action as “digital identity theft”.

Terpin co-founded BitAngels, a group for investors in Bitcoin (the world’s biggest cryptocurrency by value) in 2013, and established a digital currency fund in 2014. He is claiming for 3 million tokens stolen from him, worth $23.8 million, and an additional $200 million in other damages.

According to the complaint document, AT&T had been contacted by law enforcement authorities about similar frauds in the past.

Terpin alleged the theft occurred through a SIM swap fraud, which involves tricking a provider, in this case AT&T, to transfer a phone number to a SIM card controlled by someone else.

The fraudster can then use the phone number to reset subscriber passwords and access online accounts.

Terpin claimed that after the theft, his AT&T account was transferred to an international criminal gang.

In an emailed statement to Reuters, AT&T refuted the claims: “We dispute these allegations and look forward to presenting our case in court,” a representative stated.