Refusal to give customer feedback

Worst experience I have had at any Hi store in the history of ever! Returned a faulty powerbank a month ago already. Sales person advised it would take 21 days for the the device to be inspected before a refund or exhange can be done. It has been much more than 21 days and not even an email or call from them. I have been to the store 3 times and the reluctance from the staff, to assist me has been frustrating to say the least. Absolutely no regard for their customers. How is it possible that the sales person can take my device back say it is collected and cant even show me proof that it has been collected. Nor does any effort to even communicate feedback.