Regarding denial of Refund for defective product

I had ordered a set of earbuds from Amazon. But there were some issues with the product. The bluetooth was disconnecting frequently and the battery was getting discharged pretty quickly. As they had a 7 day replacement policy I contacted the customer service team and explained my issue. Now since there was no stock of the earphones instead of replacement he asked me to return the product and I’ll be issued a refund. The pick up date was set but due to some emergency I was unavailable for the pickup. I called them up and asked for rescheduling the date of pickup. They said that there is some internal issue on their system side due to which they’ll have to raise a complaint and asked me to wait for 4 days. After which I called them with the same issue and they assured me of help and again raised another ticket and asked me again to wait. I get an email after 2 days that product is ok and they won’t replace/return the product. I called them up and asked them regarding this and they said that it’s ok from their side. I tried explaining to them that the product I have received is defective and had I been at home that day this wouldn’t have happend and asked them to refund but they have refused to do so. I’am even ok with a replacement which is guaranteed in their policy but they have refused that as well.