Are you using Luhn-10 algorithm for CreditCard validation? If so it is wrong it seems.

[Aariv]

This is based on Luhn-10 algorithm - The algorithm works as follows

• Step 1: Start from right most digit and double to value of every second digit
• Step 2: if doubling of number results in the digit number greater than 9 than add
• digits of the product to get single digit.
• Step 3: take the sum of all digits
• Step 4: If total modulus 10 equal to 0 then it is valid credit card accoding to Luhn algorithm.