Count number of tickets per category - Replies of customers to a same thread false the count

Count number of tickets per category - Replies of customers to a same thread false the count

Hi,

I'm allocating each ticket to a category I've created (for instance "software product", "harware product")
I'd like to know how many different requests I have received for a category.

The way Zoho creates tickets makes it hard to tell:
When a customer writes an email with subject A, a ticket is created. Counting 1 ticket in category XX
When a customer writes an email with subject A, even months after the ticket has been closed, this re-opens the ticket and continues the thread. Still Counting 1 ticket in category XX, even if the 2nd email should belong in category YY.

Do you have any idea how I could change that?
For instance, is there an option for the following -> once tickets are closed, any new email received creates a new thread.