De

lete statement will not delete records immediately. It just marked records for delete. So, the space will not immediately available after delete. Eventually, btree cleaner delete records and reclaim the space.
You have couple of choice:
1)Delete records, followed by update statistics medium on that table
2)Drop and recreate the table
3)Create cluster index after load data. Basically, it will recreate the table with different partition number.
Cheers!
Sanjit Chakraborty