I didn't bother calling, but did send an email and Delta sent me the response below. After many tries, I was able to register using the link in provided. I printed the screens for documentation.
Thank you for your e-mail regarding Delta's SkyMiles program.
You need to enroll in the promotion at URL in offer/advertisement
Others use
www.delta.com/30bonusonline
Transfer Membership Rewards points to Delta SkyMiles
Your selection of Delta is appreciated, and we will always do our best to merit your confidence and support.
Sincerely,
Hanna Davis
Online Customer Support Desk