I'm sorry you are experiencing this problem, i too have this problem. There is a BIG MESS in the financial department right now at Sony ie. i cannot redeem PSN cards, or add money via my Playstation in any way, with the exceptions of a PayPal business card, which is completely foolish, and if you call customer service they will suggest you use PayPal to try to get you off the phone or at least just try to direct you here so you can be corrected on your forum etiquette.
That being said i may actually have a solution for you that worked for myself, but your actually going to need a computer, and follow the link I'm providing for you using your computer, using your PSN sign in ID when you get there, then when signed in you will click either redeem codes or add funds section on the right side of the page. Now if your card hasn't been redeemed already or has definitely been activated this will most likely work for you as it's the only process i can use to add funds to my account.
Sorry for your trouble. Please follow the yellow link.