You could ask agent if cancellation is possible since it it is the same day you subscribed and want to back off but if your card has been charged and you get your PM phone number I doubt they could do anything for you.
PM is pre-paid service and once paid you have to use it (or not) for next 30 days. I believe this is to stop abuse of system as anybody could subscribe, use it for a day and then try refund/cancellation.
