Returns

I purchased a Merona cami in XL size. I have lost a lot of weight after cancer surgery and need to return or exhange it. I took it back with what I thought was correct receipt but the clerk said it was not the correct receipt. I came home and looked for right receipt but none matched the item. the item was purchased on my REDCARD at Culver City, CA store (Westfield Mall). Is there a way I can return this item or exchange for smaller size? I would appreciate your response. thank you, Mary Ushijima