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Accepted forms of payment > http://support.apple.com/kb/HT5552

Changing Account Information > http://support.apple.com/kb/HT1918

If necessary... Contact iTunes Customer Service and request assistance

Use this Link > Apple Support iTunes Store Contact

Try the following using a Computer...

Purchase and Redeem an iTunes Gift Card and try again.

iTunes Gift Options > http://support.apple.com/kb/HT2736

How to Redeem a Code > http://support.apple.com/kb/ht1574

Note: iTunes Gift Cards are only Valid in Country of Issue.