Count only unique values with two conditions

Hi all,

I'm trying to count the amount of employee's (temp. workforce) that left last week (so that changes every week) and have invoice "" (Not "system" or "DI").
Because there are multiple rows I can't succeed to count the unique amount of employees that left last week.
I found quite a similar version somewhere else on the internet, but that one is simplified to one criteria/condition.

Please find attached an example.

=SUMPRODUCT(($A$2:$A$13>TODAY()-7)*($A$2:$A$13<=TODAY())*($B$2:$B$13="")/COUNTIFS($C$2:$C$13,$C$2:$C$13))
or
=SUMPRODUCT(($A$2:$A$13>TODAY()-7)*($A$2:$A$13<=TODAY())*($B$2:$B$13="")/(COUNTIFS($A$2:$A$13,$A$2:$A$13,$B$2:$B$13,"",$C$2:$C$13,$C$2:$C$13)+COUNTIFS($A$2:$A$13,$A$2:$A$13,$B$2:$B$13,$B$2:$B$13,$C$2:$C$13,$C$2:$C$13)))