Unfair customer service from Superbalist

I bought one full piece swimsuit and a bikini top and bottom from Superbalist. The one piece arrived in its packaging but the bikini pieces arrived without loose in the box without their usual plastic sleeves. Upon returning all three items (as they were too small), in the exact condition that I received them in, Superbalist notified me these items are non-returnable and non-exchangeable as they were not returned in a sealable condition. After some emails back and fourth with me explaining that I returned them unworn and exactly how I received them, my request for a refund is still denied.

I am a long term and loyal Superbalist shopper. I feel I have not been treated fairly, this was their mistake, not mine, and now I am loosing a lot of money because of it.