I don't think it's your fault if Meloetta is hacked. I don't want the hacked Meloetta, but I'm sure your Keldeo is fine. I didn't even think we agreed to trade Meloetta, just Keldeo. So you can attach a Mega Stone if you want, but just Keldeo is fine. I should be able to trade tonight as well, if you can.
I'm not available right now, but I will be in a couple of hours. I'll look for you then
Also, I was talking to Nightshade Aran, to whom you traded one of your Meloetta. He told me that the OT on your Meloetta is Japanese, and the name is in English. The only way for there to be a Japanese OT and an English name is via evolution - PokeBank does not change the name upon transferring; I checked with my own Japanese Victini. So I'm calling hacks again on that Meloetta. If I were you, I would go to the Hack-Check Thread and post your Meloetta there and get a second opinion about it, in particular from dewey911p if he's available.