When paying via credit card, your card issuer may decline your payment for some unknown reasons. To complete your order, you can change to another card to pay, or you can contact your bank for further information. Or you can change to PayPal to complete your payment.

There are some suggestions for the following Declined situations.
Declined (Card declined by issuer - contact card issuer to determine reason.)
1.The credit card issuing bank did not approve the transaction. This could be for insufficient funds, frozen account status, invalid credit card number or expiration date, etc. The card issuing bank does not usually provide additional details regarding the reason for the decline. You will need to contact them for further information. 
2.The transaction may have been declined based on transaction limits established by your Merchant Service Provider (MSP). Your MSP sets both per-transaction and monthly transaction amount limits for your transaction processing. You can contact your MSP for help. A phone number to your MSP should be on your most recent funding statement.

Declined (Contact card issuer to complete transaction.)
A referral to a voice authorization center was received. Please call the appropriate voice authorization number below for the card type being used:
American Express: (800) 528-2121
Visa/MasterCard: (800) 228-1122
Discover/Novus: (800) 347-1111
Diners Club: (800) 525-9040
JCB: (800) 522-9345

For international merchants (UK and AU):
To get a voice authorization:
• Please contact your Merchant Service Provider (MSP)
• If your MSP is WorldPay, please call 0845 7 600 530
Once an authorization is issued, you can then submit the transaction through the Virtual Terminal as a Capture Only transaction. To do this, the full credit card number and expiration date are needed.

Declined (AVS Mismatch) or (Card Code Mismatch)
This means the transaction was declined due to the Address Verification Service (AVS) or Card Code Verification (CCV) results. AVS compares the billing address (numerical portions) provided in a transaction with the cardholder's address on file at the credit card issuing bank. CCV compares the card code (a three- or four-digit security code that is printed on the credit card) provided in a transaction with the card code on file at the credit card issuing bank. When enabled, both services return a code to the payment gateway indicating the verification results.