Calculations with table relationships.

Morning All, 

I've added in a few tables and created the relationships between them, Image Below. 

I'm trying to create a calculation that SUM's Commission from the Policy Commission table, based on Filters from the Team and Introducer tables. 

This is what I've done currently but it doesnt return any values I have also tried wrapping the Team filter in the FILTER expression but getting the same result zero values.

CALCULATE(
            SUM('PolicyCommission'[Commission])
                ,'Team'[Teams] IN {"T-A", "T-B", "T-C"}
                ,'Introducer'[Introducers]="Company A"
        )

Any help would be greatly appreciated. 

Thank.