With two IF conditions:
- payment due date has/has not passed
- the payment has/has not been made
the AND function is your friend.
See if this works for you. Add another column (D) to test B and C
Formula in D2 (and Fill Down)
If the due date is less than (earlier than) TODAY and a cell in C is blank ("") then insert the client name (A) from that row into a D cell, else insert "".
That prepares the table for Conditional Highlighting in all Body Cells in Column A. Select the Body Cells in A.
That Rule will automatically fill and adjust to all column A Body Cells.
TODAY here in Australia is 14 March 2018 😎.
Please reply with questions.