Once you have activated an add-on, the money will be immediately deducted for a month, and the channel will be de-scrambled (so that it starts displaying) for you.
In Sun Direct, the only way to cancel add-ons is through CC. Even if the add-on is cancelled now, the money would have been already deducted (from your Sun Direct account) for a month. So, in my opinion, there is no use in cancelling the add-on now. Here is what I would suggest:
1) Call CC and ask them the exact date on which the add-on will get auto-renewed (after the current month). Do not ask them to cancel it now.
2) Call them back exactly one day before the add-on would get auto-renewed, and get it cancelled.
This way, you could at least watch the channel for the current month.