Workday Formula auto filling holiday table to the next cells

I am using the workday formula to get 15 business days after the request to extend a due date. Broker ask for an extension X day, we approve and change their invoice due date to Y Day. I wish to exclude weekends and holidays. I have my holiday table on a separate tab (Holiday) from B1 to B10.

 The formula is simple:

=workday(date of request C1),15,Holiday!B1:B10)

This works fine in a one off however when I pull the cell down to fill into the next cell below it moves my Table from B1:B10 to B2:B11. I need the fill feature to take the request date from the cell below (Column C is where I put the request date, so it stretches down C1, C2, and so on down the excel sheet). I want column C to move with the formula, but the holiday table to remain fixed.