Inverter cancellation

On the 2nd of December, I bought an inverter and batteries from sustainable Energy. After re-evaluating the order I discovered that the system would not meet my requirements. On the 3rd of December, I requested them to cancel the order and refund my payment. On the 6th of December, I received the full amount paid although they, in accordance with their terms and conditions, could withhold a 20% handling fee for cancellations.