How To Format USB Key With FDISK?

Q: How To Format USB Key With FDISK?
A: 
fdisk manages partitions. Use mkfs instead!

# FAT
mkfs.vfat /dev/sdxy # /dev/sdxy is your usb

# Or for ext4
mkfs.ext4 /dev/sdxy 

src: https://askubuntu.com/questions/86890/how-to-completely-reformat-a-usb-using-fdisk

Did this solve your issue?