MANGO has basically stollen my money

This is the worst customer service I have experienced! I paid for an order which was delivered, I then returned one item as per instruction given to me by MANGO, the courier arrived and off my item went. I waited as I had asked for a different size, I waited and I waited! I then sent numerous emails asking about my exchange, eventually I was told it had been recieved my the warehouse and I needed to wait! Over a month and NOTHING, so I phoned MANGO, so unhelpfully! I was told they had record of the collection and I must wait! After 20 or so nails with no response I took to social media, I then was told that my matter was being dealt with as they actually had never received my item? And now they were looking into the courier company which they sent? Over a week goes by and still NOTHING! I have sent mails to which I get no response again! MANGO has basically stollen my money, I returned the item in good faith and now I have paid money for which I have absolutely nothing to show for, it is rediculous, I have asked for a refund and my requests are ignored, please take this as a warning do not buy from MANGO