I mean, buying extra retainers isn't SE's fault exactly, they're supplying a service to the consumer, and you willingly bought that service. You can't willingly buy something and use it, and then turn around and cry that it's costing you money in the first place, you kind of have to and should take financial responsibility about what you do with your own money and how much you value its worth. It's not as if they're in your house holding a smoking gun to your head and forcing you to hand over your credit card here.