571 Code for Future Date

According to the IRS's Master File Codes, Transaction Code (TC) 570 reflects an

Additional Liability Pending and/or Credit Hold:  Indicates additional liability pending.

TC 571 reverses the TC 570 hold, undoing the freeze on your return, apparently on the future date you see.

I also got a notice in the mail to send proof, do this mean it was sent by mistake?

It’s possible that it was sent by mistake, but it’d be dangerous to go on that assumption.

There should be an IRS phone number on the notice you received.  Call that number to see what’s going on.  It’s probably a dedicated number of the department that sent you the notice, so you may not have to be on hold for a long period.