Said under investigation didn't call back

I keep getting the same call and it doens't say who they are. just a robot leaving a phone number to call. is this a scam?

Female robot voice. Sounds like an IRS scam. Blocked!

Just received a call from this number and the robot said that they have been trying to get in touch with me as the IRS was going to sue me and advised to call them back.  Called back from the landline, however; there was no answer.

Definitely a scam, check out this link to the IRS warning of such scams:  https://www.irs.gov/uac/IRS-Urges-Public-to-Stay-Alert-for-Scam-Phone-Calls

IRS calling to file lawsuit. LM
Did,not call,back
Scam