In addition to your “permit”, what does your lease, leashold or assured tenancy agreement say about parking? Do you have an allocated space, or does your lease etc. permit you to park in the car park? Yes, you probably need to appeal to the IAS, who will probably reject your appeal, but first of all you need to establish your legal position and whether or not a parking company has any authority to issue an invoice to you for breaking its terms, especially if you already have unfettered permission without a requirement to display a permit.