Not to be rude but, how do you know when the plant was infected? I mean, it could have happened during shipping or maybe one of the little buggers landed on the plant right outside your door. It could have happened anywhere.
I do agree that seven days is rather short. We once bought a parakeet that landed wrong and broke a wing after two weeks. The pet store had a 30 day return policy, so they did replace the bird. I waited till after we got back home to inform my girlfriend that they likely just killed the bird that we took back. I shouldn't have said anything, she got rather upset.