Hindi accent is a dead giveaway. Been well-known in the anti-scammer community for some time. They are getting better and better in disguising their voices. But you can always spot it.
IRS does not file lawsuits. Tax disputes are civil matters. 90% of all IRS tax disputes are settled administratively. IRS has absolutely no authority to call on local law enforcement for anything. Local law is never involved in IRS tax disputes. If LE is necessary, US Marshals do the job. IRS does not cold call anyone and ask for money. All contacts by the IRS are initiated by US mail.
DO NOT RETURN THEIR CALLS. The male Indian scammers become very abusive when they find their scams arn't working.