In most cases the music for Doc Group videos comes from an agency called Audio Network. Send a copy of the music cue sheet and invoice to claims@audionetwork.com and include a link to the YouTube video that recieved the copyright claim. Do not refute the claim through YouTube… that’s a last resort for when a license holder is being unresponsive. Remember, often these copyright claims are automated, not a malicious person trying to get a video taken down. Proving that we have the rights to the music is something we should expect.