If you are getting some biils for S3 resource although there is no enough data in your bucket according to you. When you check the bill, it charges you for some GB data in your s3 bucket every month but you do not remember any GB data in your bucket.
I would suggest you to check bucketobjectsize metric in s3. Open your s3 bucket and go in Management > Metrices . here you can see all occupied size of your bucket. You can open this metric in cloud using 'View in cloud' option. In the graph you can see the graph bucketsize increment over the time. This is very helpful to analyze your bucket filling capacity over time.
If you are using your s3 bucket to keep back up data, please make sure you remove older data frequently. This may be the reason your bucket is occupying too much size.
If you have used cron to put data in the bucket and same cron is used to remove data after X days of time, I would sugest you to check 'Versioning' option in the properties. If 'Versioning' is on, even if you remove the data using cron, still it keeps one copy of it and this may be the reson your bucket is showing this much occupied space.
Open s3 bucket in aws management console and enable 'show' toggle button to see all hidden data, remove this data and your bucket will be back with the expected occupied size.
