Exactly the same thing happened to me.
XM has a really poor business model. I do not know of any other business that renews without asking.
Telephone, Internet, Cable, Electricity, Gas, Water, Banking, Online gaming just to name a few off the top of my head. Many different subscription services have automatic renewals.
XM is just like the above services, and only does the bills electronically online as is becoming increasingly common. I know I don't get a bill from my bank every month now, and they don't ask me every month if I'd like to continue banking with them before they take the account fee. Same with my Rogers account, my Telus internet etc.