It would appear here that it is being alleged that you obtained a further day's parking from the same ticket. The law however requires that the prosecution proves the case, if you can show that on the 7th. you were elsewhere, in other words, corny as it sounds, you have an alibi, then you would have had no need to use the ticket on the 7th. and as in effect you issued the ticket yourself you had no reason to alter the date. Also as is stated you could easily have added a second date then surely you should not have been given a ticket. I would definately appeal, and if they are difficult ask for the act and section under which this ticket was issued to see whether it is an absolute offence, but I would be amazed if it was.