I tell any client that I meet with that their date is not secured until I receive a retainer. I’ll only do 2 weddings in a weekend, so the first 2 that pay get the day.
I would suggest modifying your contract again and adding clauses as to when the final payment is due and what date the client can no longer made changes to the design or number. I require final payment and don’t allow the client to make changes 90 days before the event.
It may not help you with this client, but it will with the next client-zilla!
Jenniffer White, Cup a Dee Cakes - http://cupadeecakes.blogspot.com