Travel company charged supplement by mistake, now refusing to refund.

[DutchGirly]

I booked a trip to Disney Paris with a travel company. The travel agent inadvertently charged a ferry supplement by mistake, the supplement was applicable if you travelled between a certain time period. However our departure time was inside the time period for which no charge was applicable. I did not notice this until a few months had passed and in April I wrote to them advising them of the mistaken extra charge and asking for a refund. No reply at all so I wrote again in September.
Today I received a letter stating that as I did not notify them of the mistake earlier, they're unable to refund me the supplement. What is the legal position here? The travel company made an error, a few months have passed and now they're refusing to refund.

How much was it for? You could take them to the small claims court. 6 years is the legal cut off point for recovering debts like this.

Are they a member of ABTA? If it was paid on a credit card you might be able to recover it from the card company if the transaction was for over £100.

The travel company is a member of ABTA. I paid by debit card. The letter refers to 'No refunds or amendments are allowed on this booking' which of course is not applicable since I did not cancel the booking, I just want to have the supplement refunded that they charged by mistake.