If you delete the sub-account on your PS3, then it will be removed from your PS3 but it will remain on Sony's server. Credit card information is stored on your Master Account, not the sub-account.
There is no way to delete accounts from Sony's server, but they can be closed permanently to prevent anybody from logging into them again.
Yes, you can have your credit card information removed. Visit the Sony Entertainment Network website and sign in. Afterwards, you can manage your account information.
Master accounts are for people ages 18+. If you remember the birth date you entered when making your accounts, that might help narrow it down.
Seems like this is my master account and i have no sub accounts. I have made new accounts from the XMB-screen, had no idea you could do that from the homepage.
If i have deleted another master account, will the credit card information be removed aswell?
You need to log in and remove your credit card information on the website. Deleting accounts from your PS3 system does not remove credit card information from Sony's online servers.