Had this happen to friends. LifeMiles locked their accounts from purchases but failed to notify them they did it. Same symptom as yours - try to book a flight and it fails on the payment every time no matter which card is used. After calling they were informed they had been locked out for suspicious activity on the account - without saying what the suspicious activity was. The phone agent forwarded their case to the account security department who emailed them a couple of days later with a request to send a photocopy of their ID to confirm they were the owner named on the account. At some point later their account was released for purchases again.