SUMX Over Distinct and Max

Thanks for the replies but unfortunately they were not working for me.
I have managed to solve it using the following measure:

Channels Total = 
SUMX( 
    VALUES ( Charges[CLI] ), 
    CALCULATE (
        CALCULATE (
            MAX ( Charges[Channels] ),
            FILTER (
                VALUES ( Charges[BillingPeriod] ),
                Charges[BillingPeriod] = MAX ( Charges[BillingPeriod] )
            )
        )
    )
)

I have updated the sample project to reflect this:

https://1drv.ms/u/s!AoTVsSI4n62qjZ0Mq4u-5-4lAzqDqw?e=mYde5a

If anyone know a more efficient way to right this then I would love to hear.

Also I'm not sure why I had to use CALCULATE twice but it was the only way I could include part of the code without having to create a seperate measure. 

If anyone has a good explanation for this then please let me know.