Can I ask how you relocked the bootloader? And when you claimed the offer, did you have a custom recovery installed?
Also, can you let me know anything else you did which would deviate from stock? It seems there are a lot of people who have rooted their phone and tried to get the Drive promo... The unlocked bootloader is a key part of having the Drive app state it cannot verify the phones' status, whereupon it gives you a link to HTC's support.
And if you try and relock the bootloader using "fastboot oem lock", it will not be a factory default lock. Based on the info you provide HTC, they will know your phone is ***RELOCKED*** and not ***LOCKED***. The promotion is officially not available if you have locked your bootloader. And there there are several reports that HTC won't budge on giving you a promo code when it determines you already unlocked your bootloader, even if it is currently locked.
I am trying to make a guide to help people get their phone to a state where they can redeem this offer if they rooted their phone (and unlocked the bootloader...especially if they used HTCDev to unlock it).
If you are S-off, you can lock, unlock, or relock by just writing to where that data is stored. The best part is, you don't trigger a data wipe in the process. IOW, once you are S-off, changing your lock state is almost as simple as changing your CID.