This is what I did to get my 50GB of drive.
[how to] remove your "tampered" banner
[how to] lock/unlock your bootloader without htcdev(s-off required)
Changes to your Google storage plan
You activated an offer to receive free Google Drive storage from your HTC smartphone and we‘re pleased to inform you that we are increasing your free storage allotment to 100GB for the remainder of your offer term.
No action is required. Your storage plan has been adjusted automatically.