Somebody uploaded my music without my permission!  How do I get it taken down? 

This can occur when another individual uses other distributors to distribute content to stores. Your best bet is to reach out to the platform or store hosting the content and request a DMCA takedown (the platform is obligated to remove the content as the issue is investigated).  Most platforms have forms to do this (e.g. https://support.spotify.com/us/account_payment_help/privacy/report-content-infringement/).

Can I distribute or monetize an unofficial remix? 

No - you can only distribute music content that you control the rights to.  Please do not attempt to distribute content where you do not control all aspects of the release (e.g. unofficial remixes, content containing uncleared samples, etc.).  However, if you want to distribute an official remix, please ensure that you get permission from the original copyright holders before distributing.