With gold status you should have been able to access that lounge. The response from the Twitter team wasn't correct, gold entitles you to access worldwide lounges, regardless if Etihad operates these or not.

Did you travel on Etihad metal or Air Berlin metal? Was your frequent flyer account linked to your ticket, in other words, did your boarding pass mention your EY guest number? Did you actually try to access the lounge or only asked at check-in and took no for an answer there?