To view the SharePoint list items that are created this month you need to create two calculated columns and a custom view.
Add a new calculated column StartMonth and at the following formula:
=DATE(YEAR([Created]), MONTH([Created]), 1)
For the second calculated column EndMonth use the following formula:
=DATE(YEAR([Due Date]), MONTH([Due Date])+1,1)-1
Now create a new view and add the following filters:
StartMonth is less than or equal to [Today]
EndMonth is greater than or equal to [Today]
now you have a view for all calls created this month.