Interesting. In this time of strife, the phone lines at Blizzard are permanently full. This being the second day that I try to reach someone to change my name (preferred) or cancel my account.
I cannot, however, reach Blizzard on the webpage either. Trying to follow the link from the homepage most of the time leads to a "failed to find this page" error.
Here you are, though: https://eu.battle.net/account/management/wow/
For us Europeans that is the link to account management on Battle.net. The "Cancel Subscription" button is near the top.