Due to the nature of our non-exclusive license and our construction kit format, Youtube and it's subcontractors sometimes find two pieces of music that are similar or have similar elements. You should contact YouTube directly and explain that you have licensed portions of your songs from Big Fish Audio. Tell them that your song is different from the 3rd party claiming ownership. Below is a template you might find useful:

"The music used in my video named ____________ was a derivative work of music with elements licensed from Big Fish Audio. Big Fish Audio provided me with the musical elements on a non-exclusive basis. The creators of other videos on Youtube using the same musical elements have also been issued a non-exclusive license from Big Fish Audio. Since I am the rightful owner of the music found on my video please remove any restrictions that you have placed on my video ___________ . "