Refund Declined!!!! I will not let this go!!!!!

So I bought a pair of sneakers for myself and my husband about 2 weeks ago. I returned the sneakers on Friday asking for a refund because they didn't fit and was to small. We tried it on ONCE and now they are telling me that it is dirty and cant refund it!!! This is unacceptable and I wont leave this lying down, I literally buy from this site on a weekly basis and hardly had issues. You guys cannot prove we are the ones that make whatever part of the sneaker dirty, as we received it, we returned it. I buy sneakers and shoes and half the time its ****** worn. I want this sorted ASAP!!!! I will be taking this further and want you guys to prove that it was never dirty to begin with.