Delayed reply from me, sorry.
I have copied and pasted the info from my email from Amex:
As a Platinum Card Member, we’re excited to offer you the unique opportunity to attain Platinum or Gold Velocity Frequent Flyer Membership for one year. Simply complete an eligible transfer of your Membership Rewards points to Velocity between 30 October and 30 November 20171.
To enjoy all of the Status benefits you have come to expect from a world-class frequent flyer program, simply:
Transfer 500,000 Membership Rewards points to upgrade to Velocity Platinum membership1.
Transfer 250,000 Membership Rewards points to upgrade to Velocity Gold membership1.
Plus as an added bonus, you will also receive 20% bonus Velocity Points.
It sounds like Velocity were incorrect in their reply. Try emailing firstname.lastname@example.org which has worked OK for me for customer service issues in the past and update us if you don’t get any luck.
Terms were as follows:
The promotion period for this offer is 30 October 2017 to 30 November 2017 (‘Promotion Period’). This offer is only available to American Express Centurion Members, American Express Platinum Card Members and American Express Platinum Business Card Members. To receive an upgrade to Platinum Velocity membership for 12 months, you must transfer a total of 500,000 Membership Rewards points in one or more transactions during the Promotion Period. To receive an upgrade to Gold Velocity membership for 12 months, you must transfer a total of 250,000 Membership Rewards points in one or more transactions during the Promotion Period. A minimum of 2,000 Membership Rewards points may be redeemed for Velocity Points at any one time. The 12 month period will commence from the end of the Promotion Period. In order to maintain your Status at the end of the 12 month period (on your Review Date), you will need to have earned the required Status Credits and flown Eligible Sectors.