I also received message about IRS lawsuit. Called back and denied them the info they were asking for. When I questioned them, they told me a warrant would be issued and hung up.
Msg left pre-recorded robotic saying that IRS wanted to file a lawsuit against me. I don't owe anything to them and file my taxes regularly and rarely have to pay anything. I called back the number and woman who answered could barely speak english and barely pronounce Internal Revenue Service. I told her to stop calling and take me off their list and she said OK. IRS would not say that.