Do not panic: This is a Fraudulent Agency!
As stated in the linkhttps://www.irs.gov/uac/report-phishing :
The IRS doesn't initiate contact with taxpayers by email, text messages or social media channels to request personal or financial information.

The best action to take is to report the incident to TIGTA and email a copy of the incident to [email protected] (Subject: 'IRS Phone Scam')
https://www.treasury.gov/tigta/contact_report_scam.shtml

They are in direct violation of several codes clearly outlined here: https://www.irs.gov/irm/part9/irm_09-001-003-cont01.html

DO NOT GIVE THEM ANY PROTECTED INFORMATION ie SSN, DOB, ADDRESS, etc!

FCRA states that a debt must be sent to you in writing in order to determine if the debt is legitimate before due-process can continue. Even clauses stating that if a response is not received in 30 days is superseded upon an FCRA dispute being issued i.e. council has to retroact to the time of disputing the debt's legitimacy.

Additionally, the ACS cannot be used until the bill, the publication 1 and publication 529 are sent you, please refer to: https://www.irs.gov/uac/the-collection-process for even more information. If you have true IRS concerns do not call this number as the IRS NEVER uses phone numbers that are not toll-free (8xx) nor will they text you (MMS/SMS). Below is the contact information also in the link.

Taxpayers may call, write, or visit the IRS:
Call the phone number on the bill or 1-800-829-1040.
Write to the office that sent the bill at the address on the bill.
Visit the nearest IRS office.

One ounce of prevention is worth a pound of cure so arm yourself with more knowledge on scam tactics at: https://www.irs.gov/uac/tax-scams-consumer-alerts