DiamondLady in - Replacement not received

I bought a 'Tropical Safari Romper' size small from an Instagram business called 'DiamondLady' for a friend of mine as a gift: however, I messed up her size. I went ahead and requested a size replacement from small to medium. The original dress in size small was delivered to me on May **, ****. The dress was picked for replacement on May **, ****, and it was handed over to the business on May **, ****.
Now as per their Exchange and Return policy mentioned on their website(https://diamondlady.in/policies/refund-policy), states - Exchanged item will be shipped once the old package reaches back to them and the entire process can take ** - ** days. Now as I can see the old package was handed to them on May **, ****. I should have received my exchange item by June * to June *, ****. Today's date is July **, ****, I have neither received my exchange item nor have they provided me with any tangible update about my exchange item. I followed up with them through email, their website chat, Instagram DM, and even their WhatsApp business number. My messages were left on read on Instagram and WhatsApp in the past with no updates whatsoever. They have replied to me on a few occasions just asking me the same information again and again with no updates. They have also asked me for the 'exchange order number' which I understand should have been generated and communicated to me before or during the collection of the dress; however, it was never given to me in the first place and now they demand that number which they never gave me should be given to them. But again they have not communicated with me on this matter whatsoever.
I have been kept in the dark for around * months now with no communication.