I want to cancel my youtubetv. It will not allow me to do it.help

Purchasing and managing auto-renewing subscriptions -

http://support.apple.com/kb/HT4098

ASC - Late 2012 Mac mini, macOS 10.14;  Watch, series 3 cellular, watchOS 5; iPad Air 2 & iPhone 8+, iOS 12; TV 4th Gen, tvOS 12;  Airport Express w/ Airplay 2

It should be canceled and not take another payment if you followed the instructions. I have no idea what your subscription time period is. You can use the subscription through to the end of the subscription period.