Extremely bad service from the usual great service...

I ordered a pair of bluetooth headphones that turned out to be faulty. I noticed they didn't charge & requested an exchange within a week or less. I was surprised when I was refunded instead of exchange. When I enquired, I was told that I will not be refunded coz there's no stock & shipping is 5-7 days at a different price from another supplier. I requested that any other colour would do but that was declined. I was told that if I want another pair, I must order it (at a higher price & pay for shipping). I find this appalling from a usually efficient company. I want a replacement & am not willing to accept the refund as I'm still under the 30 day warranty as I post this. Why must I carry the cost of replacing them at a higher price?