Did you test the WD My Passport on another MAC computer to see if it will get recognized? How any partitions does the My Passport have? I am asking you this because if you have formatted the external drive into two partitions in two file systems, you could connect it to a Windows PC in order to check if it will get recognized there.
I also would recommend you to change the cable that you connect the external drive to the MAC as it may gеt damaged.
Western Digital representative