Refund not paid

I returned my jeans at Cotton On Cavendish that I bought online, they advised I will get my refund in 3-7 working days. I called the store today to find out what is causing the delay they said I must go into the store with my 3 months bank statement and get proof of the receipt from customer service. All this for R639, they are causing an inconvenience and should have told me when I returned my clothes. I just want my refund please