I'm the same as the OP. Been subbed since 2.0, on a 180-day auto-renewing sub that renewed on or around mid-May 2017, and recently auto-renewed again a few weeks ago. Aaannd... no mount.

Based on the official Campaign Eligibility -- Note #3:
"If you have remaining subscription time that was purchased before the campaign period, or you have an active recurring subscription, we will calculate any remaining game time available as of Saturday, July 1, towards the campaign."

So, by my math - at the time of July 1st, I had 130 days remaining subscription time left on my account, and, therefore I met eligibility.

Any ideas on how to fix this? Contact customer support? ...Or post in another thread somewhere?