df command shows 100% full, even after deleting files it shows same usage (100%)

Nand Flash storage partition shows as 100% full with df command. When manually calculated the usage it is about 7-80%(max) only. Deleted few files (say around 50~60MB), still df command output did not change. I can not create a new file, error: "there is no space left on the storage device". Tried sync command, no difference. Filesystem 1K-blocks Used Available Use% Mounted on tmpfs 262144 20780 241364 8% /tmp tmpfs 512 0 512 0% /dev /dev/ubi0_0 1275540 1275540 0 100% /storage When the actual storage space is not full (as per the manual calculation), why doe df command shows it as 100% full?