I am having exactly the same issue. I never contacted Nokia, however, because first, I don't buy apps very often. Second, for all apps I wanted to buy since this started (half a year ago?), it eventually worked after trying hard . Every time this happened, Nokia Store became unresponsive a short while after I had stopped the payment. So I had to restart the phone. It then worked after some waiting or several such tries, or the next day.

Not really a solution, sorry.