It sounds to me like your subscription to XM did not download to the XM tuner in your cube yet, This is common if you called to activate the XM service and did not have the XM unit on while they sent the satellite signal to your xm tuner, If I am correct then the fix for this is as follows,
Call XM and tell them you need a refresh signal sent to your account, they will then ask you if the XM radio is turned on and tuned into channel 1, which it should be or else you will not get the satellite stream again, then they will send the refresh signal and within 30 seconds to 5 minutes the radio should update and you should have all your XM channels. I am 99.999% sure this is your problem, after 15 years in the mobile electronics business and with the popularity of satellite radio I have seen this happen numerous times. Just make sure the XM radio is on when you call them and the channels download and you will be fine,
Rick