office chair with defects

I bought an office chair there, on the 18th July. The manager there Maria was quick to push the salesperson to furnish with my purchase. Next thing there is a contract I need to sign without anybody explaining to me what I am signing for. I refused to sign and asked them to check if the chair I am buying is working first and secondly what am I signing for. Just to find out the chair is not working and the return policy was not explained. The client has 4 days to return defective products and after that, the store can only repair them. The salesperson promised to get me another chair, which he did. I asked him to assembly the chair for me before delivery. He did not do so, when I got home to assembly the chair I found out the very same chair has the same defect. I contacted him he said the reason why the chair we put on sale was because of the defect. Now I returned the chair and I have to wait 21 days for a refund? I paid cash, why must I stay another 21 days without a chair when the store intentionally sold me a defective chair intentionally?