Do you actually have that achievement though? You mentioned you have satisfied the three class requirements, but there might be something else you haven't attained yet (although according to SE's official information, that is all that is needed for them).

If you do have the actual achievement, when did you receive it? Did you attain it originally in 1.0? There was an acknowledged bug that affected a few 1.0 players where certain 1.0 titles were lost or not showing up in ARR for players despite having the achievements, so it's possible this might be the case here - SE stated you had to contact them directly (either through a GM in game or by using the Bug Report section of the forum) to get it fixed sadly.