Listbox showing data searched in a sheet using the given combobox value

Hi everyone,

I'm facing a very hard (for me) issue. Ok this is my situation:

1. my worksheet has 7 sheets, let's say DE, E, DU, U, RI, Look, M

in sheet DE I have the following data:
COL
ROW A B C D E F
1 Name Invoice num Invoice date Value When due when paid
2 John 1 01.01.17 100 01.01.17 01.01.17
3 Bill 2 01.02.17 200 01.02.17 01.01.17
4 Howard 3 01.03.17 300 01.03.17
5 Mary 4 01.04.17 150 01.04.17
6 Tina 5 01.01.17 50 01.01.17 01.01.17
7 Bill 6 01.07.17 170 01.07.17
8 John 7 01.03.17 100 01.03.17 01.01.17
9 Mary 8 01.02.17 100 01.02.17

where the name in A are set from the sheet Look, which has:

COL
ROW A
1 Name
2 John
3 Bill
4 Mary
5 Howard

So column A in sheet "Look" has a order list of unique name
Sheet DE is where I register all the invoices. So I could have, in column A, the same more times.

My issue

I created an UserForm like the following:

Userform1
Combobox1
ListBox1

and I would like that ComboBox1 is populated by the list in column A of sheet "Look" (I menaged it, more or less) and then ListBox1 is populated with all the invoices which are not paid (so with column F empty) of the given data in ComboBox1 searched in the sheet "DE".
To better explain, if in ComboBox is set the value "John", the listbox will not show anything (all the invoices are paid).
If combobox shows "Mary", then listbox1 will shows ROW 5 and 9 of the sheet DE.
What shoudl be the code for that?
Thank you in advance.
Giacomo