You can see, that the amount of occupied space used on the storage servers is bigger than the amount of the backed up data.
During backup the software creates some temporary files. These files provide redundancy for an unlikely case of a storage hardware failure during a backup operation. When the backup completes the temporary files are marked for deletion and cleanup is performed several times a day. This is expected behaviour and does not affect the storage space that you are being charged for.
You back up disks or an entire Linux machine. In the backup plan, you specify exclusions. Specified files/folders are not excluded from backup and backup completes with warning "File exclusion is not supported".