Karaca Stainless Steel Teapot Rusted - Refund Request Rejected

I bought a stainless steel teapot set from the Karaca store in İstanbul Maltepe Piazza AVM. Although it is a stainless steel product, rust formed inside the teapot after about three months of use, which I find unacceptable for this type of product. I would like a clear explanation from Karaca as to how a product that is sold as stainless steel can rust in such a short time. Because of this situation, my family and I unknowingly drank tea from a rusty teapot all this time. I find it very disturbing that we were made to consume tea from a rusted interior surface, and I believe this is a serious health concern and means our health was not protected as it should have been. When I contacted the store about the rust problem, they offered a product replacement. I did not accept this because I do not want to experience the same problem again with a different teapot set. I requested a refund, but they did not accept my request and insisted only on replacement. I am disappointed that a stainless steel Karaca product rusted in such a short time and that my refund request was rejected. I kindly request a full refund for this teapot set, a clear written explanation as to how this rusting occurred in a so‑called stainless product, and I expect this issue to be resolved as soon as possible.