Refusal to Refund

I made a purchase at Groupon (Order Number Grpzarsssvx5) in May and the item I purchased was out of stock, my banking details were forwarded to Groupon for a refund but to date I still haven't received it. On inquiry, they said they sent the refund of R399 on 30-06-2015 using reference Grpzarsssvx5.. I forwarded my bank statement as proof that I never received the refund. It has been five months now and haven't been refunded yet.