Please try the below query surely it will increase your performance.
SELECT DISTINCT
custname
,address
,street
,city
,state
,phone
,pincode
,delivered_counts
,undelivered_counts
,SMS
FROM report_table (NOLOCK)
WHERE
Identificationdate BETWEEN @StartDate AND @enddate
AND Custname = @custname
AND City = @city
AND state = @state
AND LOB = @LOB
AND prod = @prod
AND Subprod = @subprod
AND Cast(contentID as varchar(20)) = @contentID
AND AlertID = @AlertID