Mr Price and not returning full refunds

I had bought item on the MRP app...the order was not delivered because they could not locate my address, when I was supposed to be refunded I was not given a full refund and when I enquired as to why I am not getting my full refund I was told it was because one of the items was not returned back but I asked how can I return something that didn't even reach me. The person that I had spoken to said they will check with their courier guys but till today I have nothing.. Very disappointed with Mr Price