If you have attempted to enable quotas after following these guides with no success, then it likely means you have a system that utilizes UEFI firmware.
Being by testing the system you have using the following command:
[ -d '/sys/firmware/efi/' ] && echo "UEFI System" || echo "Standard BIOS System"
If your system is detected as UEFI then you will need to perform the following steps to enable quotas.
Create a backup of your EFI grub configuration:
cp -avx /boot/efi/EFI/centos/grub.cfg /boot/efi/EFI/centos/grub.cfg.$(date +%s)
Then rebuild the Grub configuration:
grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg
Once its been rebuilt, confirm that quotas appear as enabled in the new configuration:
grep quota /boot/efi/EFI/centos/grub.cfg
The expected output should look like this:
linux /vmlinuz root=UUID=bc7453b1 ro rd.auto crashkernel=auto vga=normal nomodeset rdloaddriver=raid1 rootflags=uquota
linux /vmlinu root=UUID=bc7453b1 ro rd.auto crashkernel=auto vga=normal nomodeset rdloaddriver=raid1 rootflags=uquota
Finally reboot your server.