In telephone calls carried out in Chinese, the scammers reel in targets under the pretense that they have unpaid bills related to recent surgical procedures. They use spoofed telephone numbers belonging to the claims departments of legitimate US health insurance providers to add a layer of authenticity to the scam, but that authenticity quickly evaporates. If, for some reason, targets entertain the conversation about paying for a surgery they almost certainly did not receive, the scammers get them to join a video call.
Tax calculations can be, well, taxing, so a message from HMRC saying that there's been a mistake may not ring too many alarm bells. Some bring good news: you have overpaid and are owed a refund, but others claim you owe money. In both cases there's an imminent deadline to act sometimes with the threat of legal action, or penalties if you don't. Scammers are taking advantage of people's fears over bills to steal personal and banking information.