CiviDiscount Isn't Tracking Usage
I'll ad this as an answer so it's not lost in a comment. 
Steps to figure this out would be:


CiviDiscount is installed on demo/dmaster: try and reproduce your scenario/bug on demo/dmaster - starting by adding discount config here: http://dmaster.demo.civicrm.org/civicrm/cividiscount
If you can reproduce the issue you're seeing on:
http://dmaster.demo.civicrm.org/civicrm - then file an issue here:
https://github.com/dlobo/org.civicrm.module.cividiscount/issues
If things are working properly on http://dmaster.demo.civicrm.org/civicrm - the issue may have been resolved and you would then look at upgrading your own instance to that CiviCRM version/CiviDiscount version.


All the best!