Pavani, here from iTunes Store Customer Support team. I understand that you are unable to make purchases using your iTunes Store account. I know how it feels you that you want to buy something, but you can’t. I will be happy to look into this for you.
Thanakan, for your information, we use technologies to protect your account that may be encountered during normal usage. We've made some changes on our end, so the issue should be resolved now. Please logout completely from your iTunes Store account and wait for 30 minutes before login again to make purchases. We appreciate your patience. If you still can't purchase after trying again, let me know. I’ll be happy to help.
I hope my response was helpful. If you have any further questions, feel free to write back to me. Thank you for being in iTunes family.