I drove 400km to not get a product exchanged

I was gifted linen from Loads of Living for my wedding in April. One of the duvet covers is a Queen size, and I need a King. 

Because I live 400km away from the closest Loads of Living store, I was only able to drive to Loads of Living in Menlyn this weekend (at astronomical cost). 

The desk agent refused to exchange the duvet cover, even after I explained that I was not able to return it earlier because I live in a rural area some 400km away. She said it was "policy". I asked, politely, if she could call Customer Services; she refused.

I am now sitting with a beautiful 400 TC Bamboo duvet cover that I cannot use because it is too small, and although Loads of Living still has stock of this particular style on their shelves, they are refusing to exchange it for a King size cover.

While I can understand that the policy says returns and exchanges are accepted until 30 days after purchase, clearly this is a unique situation. The company's service is shocking.