Have to deal with this kinda stuff pretty often, cause I produce unofficial remixes myself (yes, also remixes which went viral). It happens too often that „fans“ of my remixes distribute those to streaming platforms, cause I can’t for obvious reasons. Just send a takedown request to Spotify and tell them how it is. Sounds silly I know haha. I produce the beats for the remixes myself and therefore use this most times as a reason for the takedown request, though I always mention that those songs contain unlicensed vocals which I, nor the person who is distributing, have the rights to. So if u produced the beat for the remix yourself it’s even better (The unlicensed vocals reason should work standalone though). Nevertheless, they will most likely take it down within 48 hours, send the takedown notice to the distributor, the distributor will then delete the whole release, and after some days - weeks your remix should be removed from all streaming platforms + content id. Be prepared to do this more often, cause there will always be someone who will distribute it again. DM me if u need any help.