What tactics do SiriusXM employ to retain you? When my trial expired, they just sent me a few snail mails begging for money. Easy enough to bin.
OnStar required calling to cancel. They provide a web UI where you can add a new payment method but you can not remove all payment methods or cancel. Once you've convinced the person on the phone that you want to cancel, a new option to remove your payment method appears in the UI. The person on the phone didn't tell me to go back to the UI, I was just paranoid and saw it by accident.
I'd read enough horror stories on consumer affairs with, for example, people still being charged after they canceled.