Wait until much closer to the stay date and politely request again, i.e. you would like the upgrade on arrival if the room type is available. We're 8 months out from August so they're inclined to sit on their better inventory, but have no reason to do so a week from the stay if they have inventory they likely will not fill (or don't have other more "worthy" elites to give the upgrade to).
Generally I've found success close to the stay date or on site with both with Marriott and Hilton.