how do i update my credit card info on itunes

I am also having this problem and it is drving me insane i have tried everything

Did you get a solution?

I am having the same issue-did any of you get an answer to this problem yet?

I have the same problem. Any one have a solution yet??

I am having this problem too - I've tried to use several different cards and I am definitely entering the correct information and security codes - but I keep getting a message on itunes in red that says "For assistance, contact iTunes support at www.apple.com/support/itunes/ww/." I get the same message whether I'm on iTunes for Mac or on my iPod touch.