I just cancelled my XM subscription a couple of weeks ago. Not worth the money anymore. And then XM refused to allow me to cancel online and tried forcing me to call them. After waiting on hold for a few minutes, I gave up, sent them another email, and when they again told me I had to call to cancel, I disputed the charge on my credit card and Chase reversed the charges for me. Done.
Sirius/XM is struggling and they're not helping themselves at all.