new credit card log in

i lost my old credit card in an ATM, (iam in Adelaide in the state of South Australa) have tried to access on line buying and downloads ( i cannot even get free downloads because it keeps wanting my old card number) but every time i put my new card number in, it is rejected, can any one tell me how to change my card details: Have been to Apple ID but still every time my new number goes into change it from the old number to the new my card number, the site keeps saying "Security Code" does not match my card number...

Redroo