I've bought 10+ games on steam and they've all downloaded without problem.
- Have you read the FAQ? There might be something there about it or what to do
- Perhaps your firewall is too strict
- Perhaps your ISP doesn't allow it
- Perhaps your CC is from another country then you're trying to download too
- How long have you given them to respond? 1 day 2 days? 1 week?
I've personally found Steam to be fairly efficient, and if something isn't working they do what they can to fix it. Also why block on your CC? WHy not just ask them for a refund? If you block on your CC you are just giving yourself a bad record with steam, if you ask for a refund because x doesn't download IMO that's a lot better and makes more sense.