Just to confirm, have you tried reporting them under "Report spam or abuse" option to report spam comments? Also, you could block a user using these steps: https://goo.gl/Dm8S1t . Let us know if this helps!
The commentor has the same power as you do, though may disagree the most you can do atm is report, block and ignore him to your best abilities and youtube will do what is expected of them or as they see fit.