Thanks for your helpful votes - for those that have suffered because of store-credits actions - take these IMMEDIATE steps
Phone your bank - stop your debit card - report it lost/stolen/damaged get a replacement issued - the new card will have a different number and will prevent store credit attempting to take money.
Ask your bank to stop any direct debits standing orders to store credit.
Phone Action Fraud *******040 - explain the problem - get a Crime Reference Number - give that to your bank. Action Fraud are run by the City of London Police - they are a very very powerful and effective organisation. They are also on line.
Regards
Steve