It was impossible to change my method of payment via my account, not to mention that it was not possible to opt out.
Ultimately, after consulting with the bank that issued the credit card, I cancelled the card and got a new number.
You bumped into a little known "hitch" when giving authorization to assign payments to your credit card. Once you have done so, you cannot take away the authorization ....only the organization to whom you've assigned the right can do so.
When I learned that, I started being very careful about allowing "regular charges" to my card.
