This is unfortunate,
You can use the feedback link at the top right of this page and send a message directly to Magix support for this site. They are responsible for removing your song and can help you further.
Keep in mind that not all samples are royalty free or without copyright - this has always been. Some collections are only for private use. Make sure your read the license agreement of your sample collection carefully before incorporating into a song.
Here is a kicker for ya: according to copyright laws - Karaoke and Midi versions of songs are illegal too unless they are properly licensed. Just removing the vocals from a song does not give you the right to post it or reproduce it.
I can provide the link to this information for those who'd like more info.