Please specify which reports and the time period involved (interval, daily, weekly, monthly). Keep in mind that comparing interval reports will rarely tie out. You should only compare interval reports to see that you are in the ballpark (as I suspect you are). The reason being that calls arrive randomly and some are in progress before and after the interval making a direct comparison impossible.
You would be better off comparing daily reports keeping in mind you can still have issues if calls enter the system before midnight one day and complete after midnight the next morning.
Often end users who are having trouble understanding (believing) the report data come up with these questions. To cover their own misunderstanding(s) , they seek to "prove" the reports false and thus are not worth understanding.
This is a perfect example of the phrase "tilting at windmills". In other words a complete waste of time.