There was no attempt to avoid payment or gain any advantage — just a simple input error.
Do you think this is something worth pursuing on the basis of a minor keying error and genuine compliance?
Yes.
Is it still at pre-nto - ie nothing has come through the post.
Go on to the council website, explain what happened and just ask if they can cancel it.
Also if it is still "pre NTO" you can make the appeal. And don't panic about paying because you are waiting a response, the process is frozen until they reply and the discount remains in place for 14 days after they reply. (That's basically just not assuming a cancellation is a foregone conclusion)