Why am I now getting a letter from the IRS saying a tax warrant is being issued unless I pay $395 by end of October.

First make sure this is a legit notice ... I doubt a warrant for your arrest would happen for just $395. Valid IRS notices do not threaten you with jail or arrest. 

Read the notice carefully ... in the upper corner of the first page ... what are the numbers after CP or LTR?  And what tax year is being referenced ?   

There is no such thing as a "tax warrant".   A tax levy maybe but only if you have ignored at least three prior notices to pay owed tax.  

Sounds like  scam.

you can use the link below to register with the IRS and then check the status of your account for the year involved. 

https://www.irs.gov/payments/view-your-tax-account  

However, I would agree with others, that unless you ignored prior IRS notices, it's a scam.