I had great results switching my payment method to recurring via PayPal and then using the PayPal interface to cancel the recurring charge, FWIW. Any time a merchant with recurring charges lets you use PayPal you can usually cancel the subscription in that way.
I did the same for a magazine that made cancellation all but impossible, using a virtual credit card. I switched the payment method for the subscription and set the card to deny all charges. Then I just had to endure two months of "you're losing access to your subscription" spam. :/