After expanding your disk, df from the command-line and the WHM are not reporting the added disk space.
While we do recommend reaching out to your system administrator to verify the disk setup is correct, you can use tune2fs and resize2fs to verify if there is reserved space and expand the disk.
If the partition is currently mounted, you will need to unmount the partition first. Please make sure the partition is not actively being used and is not a primary system partition. If it is, you may need to take additional steps not covered by this guide. We highly advise consulting with your system administrator before making any partition related changes.
# umount /dev/sda
Next, run a fsck on the unmounted file system to verify there are no bad blocks.
# e2fsck /dev/sda
e2fsck 1.41.12 (06-Aug-2020)
Pass 1:Checking inodes, blocks, and sizes
Pass 2:Checking directory structure
Pass 3:Checking directory connectivity
Pass 4:Checking reference counts
Pass 5:Checking group sumary information
ext4-1:11/131072 files (0.0% non-contiguous),27050/524128 blocks
Resize the file system with the resize2fs /dev/device command.
# resize2fs /dev/sda
resize2fs 1.41.12 (17-May-2010)
Resizing the filesystem on /dev/ada to 524128 (1k) blocks.
The filesystem on /dev/sda is now 524128 blocks long.
The following block sizes are accepted:
S - 512 byte sectors
K - kilobytes
M - megabytes
G - gigabytes
Finally, mount the partition again.
# mount /dev/sda /home
For additional information, please refer to Red Hat's Documentation, How to Grow an ext2/3/4 File System with resize2fs