Thats becuase you probably wont have anything that is equal to the date being used in the where clause

You really need to do an >= < where clause

SELECT [Invoice_Date]

,[UserId]

,[Customer]

,[InvoiceNo]

,[Description]

,[Pack]

,[PIP_Code]

,[Class]

,[Major_Grp]

,[Invoice_Val]

,[Cost_Pr]

,[Quantity]

FROM [Telesales].[dbo].[Sales]

Where Invoice_Date >= dateadd(dd, datediff(dd, 0, GETDATE()) - 1, 0)

AND Invoice_Date < dateadd(dd, datediff(dd, 0, GETDATE()), 0)

Remember that dates are forever moving values

No two runs of the query are the same when using = and getdate() as the time stamp will change on each run.