Superbalist Negligence

I am extremely disappointed by the treatment I have received from Superbalist. I returned items to Superbalist on the 31st of Jan, a few days later I received an email stating, that they did not receive 1 of the items, even though the delivery guy collected both items from me. I respond to let them know that both items were collected from my premises. I received no response. I follow up, then I am told that my refund is held up by the missing item at the warehouse. Who’s fault is that? Now I’m suffering because of their negligence. I did not expect this at all from Superbalist at all, they’ve definitely lost me as a customer.