It happened to me too.

So i called up my Credit Card company, which is Citibank, and ask them if their system has received any transaction from Sony Playstation Store. They said yes, but they denied it thinking they were fraud transactions.

Then i asked them to allow these transactions to go thru again in the future. And i demanded them to make a remark on their system on my account that any transaction coming from Sony Playstation Store from Hong Kong, Singapore, US/Canada, Europe, and Japan are to be MADE VALID.

PSN Stores of different countries coz we can all access PSN Stores of different countries.

Then my transactions are ok dy. I added credits to my Wallet. No problem now.
*** Notice ***
So far I only manage to do it from PSN-SG and PSN-US. PSN-SG no problem, but PSN-US does not accept the same credit card iam using. I will try other 'brands' of credit cards later.

Conclusion: Credit Card companies will think they are frauds so u have to let them know that u're initiating them.

Hope that helps.