Am I being bullied by Junkin or are they correct (copyright Issue)

A Licensing Company put a claim on one of my videos. I disputed and emailed them telling them I had a signed agreement form to use the short 20 seconds of footage in my 10 minute video which was submitted via a google form by the owner of the video content in question. The owner sold the clip about a month later which is when this company put the claim on my video.

Now someone in the copyright department has come back saying that my claim is invalid because the person who sent in the clip is a minor and my permission agreement doesn't have the signature of a legal guardian/parent.

As usual they are being scum of the earth difficult. Not sure if I should continue fighting this or just delete, re edit, and re upload the video as it feels like the usual bullying tactics and nobody at Youtube wants to get involved blah blah blah

By allowing them to claim this video... they in turn are committing copyright fraud by licensing 100% of it for a video they only have 5% of the rights to.