It was my first time ordering from SHEIN , it’s been over a month I haven’t received my order

It was my first time ordering from SHEIN , it’s been over a month I haven’t received my order . I thought maybe orders take that long to be delivered but no they say it has already been delivered and now when I enquire about it they say I should call courier. How do I call courier when I had placed an order with them and they say no refund, reshipment or exchange because I received the order which I did not . It is their job to make investigations and get back to me with positive feedback. They are ruining their company’s reputation by ****ming customers.