1) What he does with the songs you give him, is up to him. If he wishes to sell them to other customers, as long as you didn't tell him not to, is okay. If you agreed he wouldn't resell, or you warned him about it, then please tell me.
2)Okay, if you think your low quality package will only work for individual releases why don't you tell him beforehand? I dont really get this part of your argument, you call your songs low quality, tell him 5 at a time will work, but why didnt you tell him all this before he paid?
3) If you are unsure of his ways of uploading and think he's uploading fake songs to mess with you and scam you, then tell him exactly what to do to prove it to you? Would you want him to do it with you, live? Would you like to upload the songs for him?
You keep going in circles blaming him for not knowing how to upload the songs in a smart way but you didn't tell him about any of this prior to his purchase, if the songs can't be uploaded in groups because of their similarity, then you should have mentioned this, whether he buys the songs for himself or not, this is very relevant to the deal you are making.
And to add on to this, you are claiming you won't refund more than half because you cant know if he's doing it properly or not. Okay, so tell him how to do it properly. If he does it your way, and it gets rejected all the same, then it's most likely not a problem with his ways but with the songs. And that is your problem.
Arrange a time with him so that you can tell him exactly what you need him to do in order to prove to you what is happening, whether it's any of the options I gave before or another alternative you think of, that's up to you.
I offered a solution. He can publish more than one single. Instead of a single EP.