how do i know my security code for my payment bill?

Apple ID security issues -

Call Apple Care and ask for the Account Security Team. They can assist you with your issue.

There is a short sequence of numbers on the back of a credit card, usually in thick black type. Here in the UK, the last three numbers are the security code. If you don't follow this, do not publish those numbers to try to get confirmation. Ask your bank or the card supplier.

I think I am bit late to answer you but I had the problem half an hour ago. The security code is the last three digits on the back of your credit card. It is also known as Card Verification Code.