It doesn't seem like you're doing anything wrong, but if you can't breed to get a Feebas with Dragon Pulse and you have a Female Feebas and a compatible Male breeding partner with Dragon Pulse, it may be because their are too many moves the baby can inherit.
I would suggest going to the Move Deleter which is in Dendemille Town in Pokémon X and Y and getting rid of some of the mother's and father's moves besides Dragon Pulse (as it seems their only purpose is to breed so you can get a Dragon Pulse Feebas, so it doesn't really matter about their moves right?)
>If this would result in the baby possessing more than four moves, the moves take priority in the order listed: Volt Tackle, mother's Egg moves, father's Egg moves, TM and HM moves, inherited level-up moves, baby's default moveset. The moves passed down will ordered on the baby Pokémon by the priority listed above.
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