I didn't do thru mypoints, I used cashduck.
I received my credit ($21) about 2 days after the free trial period was over (I think 2 weeks?).
I kept the service though. We get about 2 movies a week and my daughter watches alot on her laptop, so we wind up getting around 15-20 movies a month for $9 Pretty good deal!
Make sure you don't use a prepaid credit card / gift card, I think that will hurt chance of getting credit (this rule is different for different advertisers though, so not might work, might not).