Yeah I was going to ask the same question. I know I have it on my Blackberry and I certainly don't remember paying for it. Nor would I really, given that BBM is free and available on Android, Blackberry 10 and iOS.
You got the first year for free, then you should've paid, but the free subscription just kept extending itself as long as you didn't. If you check you Account/ Settings within the app it'll give you a date when your subscription 'runs out'.