Error reporting monthly tickets

[Riluin]

Hello everyone,

I'm using OTRS 3.3.9. I need to generate report monthly for everyone of my customer.
The aim is to generate reports with all the tickets open by every customer and closed in a determinate period (closed successfully).

I create my own report in Stat Module, with all the configuration I need ( such as some of the Attributes to be printed in the X-axis, restricting my search to just the tickets with the state I want). Unfortunately, when I put in the 'Restrictions' the 'The Create Time', in order to have only the tickets in a determinate month... OTRS gives me only empty sheets.
Instead of doing this, I've tried not to put a period, but leaving the default period and OTRS gives me the list of all the ticket!

How can I generate a report with Restriction to just a determinate period, for example a month, as I need?
Is there something I did not do correctly?

Regards,
Riluin