Are you using an Eeveelution in Pokémon X&Y? Have you used other Eeveelutions in other versions before?
-I have used in FireRed a whole team filled with Eeveelutions it was
Umbreon named Azazel (traded from FireRed to Emerald then back again)-Level 100
Jolteon named Dazzle-level 84
Vaporeon no name-level 80
Espion named Pride-level 79
Flareon named Fyre-level 80
Shiny Eevee named Djinn-level 80
Currently that shiny eevee was passed over to my emerald right at the beginning to help with my adventure once Hoenn was complete and Diamond came out... Djinn left the Hoenn Region and went to Sinnoh, then he went over to Unova to begin his next journey before being becoming my Main and basically finishing every gym for me and THEN it was traded over to black 2 for another run of all the gyms and elite four he is now level 100 and recides in valiantly behind me before I decide to make the ascent of Mount Silver, then Djinn will go to back to my character on Leaf Green to help in my breeding.