Purchase Dilemmas!!

I bought a pair of Freddy jeans on their online sale and ordered a size Small only to realise that I am in fact a size Medium. Upon enquiring, I was told that I cannot get a refund so I purchased a size Medium pair of gym leggings and tank top as I know knew my size was Medium. Upon trying them on they were absolute massive and that with the huge sizing I probably wouldn't even be able to fit into their Small as that would even be too big! I'm now in the same dilemma as previously, yet this time is not my fault insofar as their incorrect sizing. How can their jeans be completely different sizing to their leggings? Their after sales service was previously non-existent or understanding. This time unless I receive a favourable response, I will be taking this further as I have been more than understanding insofar as my first purchase. I will keep you updated on their response!