I have received a parking charge of £60 for not paying the parking fee. I did pay the fee but as it was difficult to enter the registration I inadvertently entered a letter E in error of the letter F. I realised this after the ticket was issued. I have written to them giving this information but they are upholding the charge. I did not avoid paying the parking charge and feel aggrieved that I should be penalised for making a simple error on a difficult machine. Should I further contest the charge?