Nwj Mayb be selling gold to consumers with incorrect weight which affect valuation

Hi on 25 June 2017 I purchased a gents ring, the only reason I bought that specific ring was because when the Sales consultant weighed the ring it was 12.3 grams of 9ct gold which I thought was a good deal for that price she also noted the weight on my lay buy contact which I took a picture of. After paying off my lay buy in December 2017 and before the ring could be sent for resizing we had it weighed and it reflected approximately 5 grams of gold. I am under the impression that the ring was swapped as it felt lighter compared to when we purchased it.

After hearing from head office I was told that no one can help me. All I want now is a full cash refund so that I can purchase a ring from a reputable store. I will never buy an anything from Nwj ever again and I shall advise friends and family as such as well.