if they use something abrasive while cleaning it will destroy the heating elements - but just to make sure - have you checked all fuses and defog relay - for operation.
If the elements have not been destroyed - you can use an electric transfer paint and see where each - element has broken, repair one at a time. - I believe that the 05 citys rear pillar moulding scratches the heater element breaking them all at once.
There was a thread here somewhere on repairing it. And I beleive the person had the exact same problem as yours