Oh Ray that is frustrating. Remember tho with a pet store purchase the odds are sometimes just stacked against you. We got ours from a pet store and consider ourselves lucky that we ended up with a healthy snake but that's so often just not the case. None of us will ever know what a young snake has gone through before getting into that pet store tank and often the store won't even tell you where the snake actually came from.
You might want to consider taking a store credit for the snake if they won't refund your money or give you a replacement that is actually feeding well (insist on being there to see it feed first). You could consider buying another baby from a breeder, then using the store credit for feeders for the new snake.
I hope that you are able to sort Felix out but if not, then I hope you can get another snake and have a better experience. They really are great snakes and I'm sorry you're having such a hard time with your first one.
~~Jo~~