NEVER put your credit card info on your PSN account. If you do, you expose yourself to situations where if your account is stolen, the thief can do a bunch of purchases, and then once you get back your account, Sony will NOT refund you those unwanted purchases and you can't do anything about it. By not having your CC info on your account, you avoid that possibility altogether.
In many countries you can use PayPal to add funds. It's not as convenient as direct credit card payment but it's still quick and easy. USE THAT OPTION. And if it's not, buy prepaid cards. Just never put your CC info on your account, EVER.