callstats.io offers two modes for your app:
In production mode, all the user minutes monitored by callstats.io is chargeable. The data retention will be based on the pricing plan you have chosen.
In testing mode, all the user minutes monitored by callstats.io is NOT chargeable. The data retention will be the same as Dev plan.
If you are moving your deployment from testing to production then don't forget to change the mode of your app from testing to production.
You can check your app mode by going to the general page of app settings.