Sizing guide is not accurate and no refund possible

As there are very few maternity and nursing brands out there, I was so excited to find this online shop. The quality really is amazing and I don’t take anything away from that. My problem is their returns policy is against CPA and really is shocking. I checked their sizing guide and bought 3 dresses according to my size. The dresses do not fit me well, they fit in some places and not in others. They offered store credit or to swop the items which make no sense as their sizing clearly doesn’t work for me. How can it not be possible to get a refund? Even if I ship the products back to them? It’s makes no sense and really leaves a bitter taste in your mouth. Also the pictures don’t look the same as what was received.