Issue with DAX - Returns the same data against every record

mayurbajaj - you can try this:

VAR meter = 
	SELECTEDVALUE( 'Bill Header'[Site Meter Identifier] )
VAR account_num = 
	SELECTEDVALUE( 'Bill Header'[Account Number] )
VAR calc = 
	CALCULATE (
        MAX ( 'Bill Header'[Bill Start Date] ),
        FILTER ( ALL ( 'Bill Header' ), 'Bill Header'[Site Meter Identifier] = meter, 'Bill Header'[Account Number] = account_num )
    )	
RETURN
    calc

If this works, please mark it as the solution.