Generic months in a graph

I need to generate a graph as follows:
I have a table with two date fields. The first is DataCriacao, which has the opening of so-called dates. The other is DataConclusao, with the dates on which the calls were closed.
But an open call in January, for example, is not necessarily closed in January.
I need to create a graphic that runs from January to December and that I can count the open calls and closed every month.
As it is now I can not, because the dates do not add up. I need to create a table or something generic dates.