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.
If you stay on the line long enough they will ask you how you want to handle this matter. Then they'll say something about you having to go to someplace nearby and buy "vouchers" by which he or she means Green dot money paks which are untraceable. That the whole thing will go away.