Trendyol NetWork Does Not Give My Money Back

I purchased two items from Network through Trendyol: a swimsuit and a bikini. However, when my package arrived, only the swimsuit was included; the bikini was missing. I immediately contacted Network and Trendyol assistant to request a refund or the missing product. The store initially responded that they couldn't supply the item and instructed me to contact Trendyol for a refund. I did so and submitted a request, but three days later, the store contradicted their previous statement, claiming the item had been sent.

What should I do now? I've followed all their instructions and contacted the store, but they keep sending standard messages without addressing my issue. Trendyol just says they are sorry. Now I'm left with only one item and an unrefunded amount of 1300₺. No one is helping, and I'm stuck in this situation. I urgently need a resolution!