That's the pain with digital purchases. They don't always transfer easily or free, if at all, to other providers.
For example, I had 15 movies on Target Ticket. They shut down the site a few months ago and all of my movies were supposed to be transferred to CinemaNow. I OK'ed the transfer and my Target Ticket account shows all of the transfers were completed successfully. But in my CinemaNow account, it shows I have nothing. I contacted support several times. They say to wait and it'll come through eventually. That was 4 months ago.
I fear the same thing could happen with any digital content providers. I have different music and movies across several providers now, including UltraViolet, Google Play, iTunes, Amazon Music, and probably a few others that I forgot about. I try not to buy any digital content any more. It may be a convenience, but when you lose an entire library, it leaves a mark that you won't soon forget.