I'm sorry to hear about the difficulties that you've experienced when trying to use your PayPal Credit. If you haven't already, please add a bank account to your profile, so that we can help a bit more on the side of security. You also may be running into our security system if your purchase attempts are out of your typical spending behavior.
If these items don't help, please feel free to give us a call so that we can look into your payment attempts more specifically. You can find our phone number by clicking "Help & Contact" at the bottom of the PayPal website.