Tables that have a pattern of many inserts and deletes tend to have a problem with accumulating ghost records (a row which is marked as deleted but not actually removed, there is a later asynchronous process that is supposed to come along and clean them up - but it can fall behind).
If you run this query and post the results we should be able to see if this is what is causing your issue.
select
sum(record_count) as records,
SUM(PAGE_COUNT) AS pages,
sum(ghost_record_count) as ghost_records,
sum(version_ghost_record_count) as version_ghost_records
from sys.dm_db_index_physical_stats(
db_id(), object_id('dbo.yourtable'), default, default, 'detailed')
where index_id = 1
