My apple snail and every one of my bettas got along. The reason he attacked it, is to see what would happen. The snail usually will retract, because it's a safety method of course. The reason the betta is aggressive, is because the snail is in HIS territory. In any introduction of betta and another critter, you have to introducde the betta into THEIR territory, not the other way around. Try taking the betta out, rearrange plants and ornaments, and put him back in. See what happens. If this does not work, you may need to return the apple snail :(
Breed for the breed, not for the money; the words any REAL breeder would understand.
You must know nothing in order to know all, for all is nothing and nothing is for all.