At 5 months most pups should have already lost baby teeth and started to grow adult teeth.

Sorry you are in this situation and it makes me mad the governing bodies only solution is return the pup for another or full refund. These are pets there should be a policy saying you must receive a full refund for thr pup or all medical bills paid for this condition by the breeder because they sold you the pup knowing full well it had problems. I would keep following this up with the breeder.