how to convert string into readable format for =DATEVALUE?

Hi all,

please view attached workbook to understand what i'm talking about!
Sample Workbook.xlsx

I imported billing dates into my master file (column B), using logic in excel I broke up the string of the billing period to properly identify the Start and End dates. Now I would like to convert these strings in columns D and E into actual recognized dates in Excel so I can reference these dates in =netwokringdays and other formulas. I tried using the =DATEVALUE function but it returns a #VALUE error. I am not sure why because the format mm/dd/yyyy is one that the function should recognize.

can someone tell me how to convert columns D and E into Excel Dates using a formula, not manually? maybe it is the syntax that is wrong? maybe there is another formula that can be used? I am really stuck here and could use any help appreciate your time guys

incase you can't open the file here is a capture of the worksheet
Capture.PNG