Refund not paid back

Deposit not refunded: Almost 30 days after returning rental car we have still not received a refund. Have been told by Amex UK that amount has been charged to our account instead of being refunded. Very clever this - imagine if Thrifty hold back on 10000 refunds that are due for an extra month, how much interest they earn on money that isn't rightfully theirs!! Will NEVER use this company again.