From the posts in this forum, I noticed that all those that got the 3 months free period again for another 3 month period had done so by canceling the package prior to the end of the original 3 month period. I had the HD Pack for the 3 months free period and then for 1 1/2 months @ $4.99. After reading the posts in this forum, I decided to try to cancel and resubscribe for the free period even though I was now paying for the package. I cancelled on line and was informed I would get a $2.99 credit on my next bill. The package was removed from my account profile. A few minutes later, I tried to add the free package again and I got a message indicating I was already subscribed. I checked my account and I had the 3 months free offer again!
So you don't have to cancel within the 3 month free period to get it free again, although you will be charged for the non-free portion of your subscription.
BTW, I like the package. I'll like it even more if they add the Epix channels (movies) like Dish has in theirs.