Use Data Validation to ensure the product code of "Sold Items" is not entered again

I have a excel file by which I make my invoices.

Here are the steps which I follow:

* In sheet "Product" I enter the product code and the item description.
*I save the excel file and close it.
*When customer want to buy a product, then I open sheet "Invoice", enter the product code in range "B11:B31" , then I enter the rate at which I want to sell the product in range "Q11:Q31"
*Then I press "Update Button" - It copies data from my "invoice" sheet to " Invoice data" sheet and saves the excel file.
*If the customer pays the amount then I click on "Paid" button and if its outstanding then I press "Due" button. These 2 button "save as" the excel file to a specified location.

So even if the product is sold , I can still enter the same product code in sheet "invoice" and make invoices. Practically the product is sold.

So through "Data Validation" I was looking for something in which If the product is sold then sheet "Invoice" Range "b11:b31" does not allow the user to enter the "product code" which is sold.

Sheet "Invoice data" is the sheet where sales is recorded. In sheet "Invoice data" range "F" contains all the codes of products which are sold.


I have attached the sample file for simplification.

Please help me if possible.

Thank You.