YouTube review: Copyright

Hi, we have a copyright issue on YouTube.

We are a religious community and we are broadcasting our religious celebrations regularly on YouTube. In this celebration the community is chanting 1500 year old religious chants. I assume that chants fall under the category public domain. Now someone recorded a community somewhere singing that chants and uploaded it on his YouTube channel and claiming copyright for it. Since years that guy is bothering us with his copyright claims on each live broadcast. I dispute his copyright claims each time and write him each time that he can't claim copyright for that chants. But he doesn't stop. His channel has no followers and no views whereas we have many thousands. Therefore I assume he only tries to make money out of it. I complaint to YouTube about it but YouTube doesn't want to do anything. YouTube answered me that if I think I am the copyright owner of that content I can file a complaint with their form. But I can't claim copyright on an ancient religious chant as much as the other channel can't do it. Can you help me with this case? Thank you so much.