BAD SERVICE. NOT REFUNDING MONEY BACK TO ME

I am very disappointing in the fact that they do not take situations serious. A payment was made wrongfully to their account of which was not even my mistake. It was an employee of PEP Stores. I am struggling for two weeks now to get my money refunded back to me. They don't reply to emails nor answer questions over the phone and they do not assist in solving the issue. It is a lot of money that i need to get back