You can't get out of a PCN by creating a backdated hire agreement which didn't exist at the time of the alleged offence.
Having said that, this probably is the right place, but at the moment you've given us nothing to go on, we don't know which authority and jurisdiction this is in. Start by reading the post titled "READ THIS FIRST - **BEFORE POSTING YOUR CASE!**" which tells you what you need to post to get advice.