Dissuade users from sending in multiple tickets

We're currently trying to decrease our one-touch ticket rate and a large number of our tickets are merging duplicate tickets from the same user - sometimes users will send 2 - 5 tickets at a time. I'd like to dissuade users from sending in multiple tickets but I'm having some trouble finding some best practices.

We've included in our auto-response our business hours (so they know when to expect a response) and a message urging them not to send duplicate tickets, but there's been a minimal change. 

This is our current messaging:

We try to get back to everyone as soon as possible, and you can expect a response in 12-48 hours. Please note our business hours are 9 AM-5 PM EST, Monday-Friday. Please do not send another ticket as this will move your request down in the priority queue. <Sending multiple tickets will slow us down in responding. If you have additional information to add, you can reply directly to this email. If you’re unsure about the status of your ticket, you can check it following the steps in our article here. 

Any tips would be wildly helpful! Is there a way to prevent a user from sending in another ticket for a specific time period once they've already sent one?