I requested a refund on an unopened part

I requested a refund on an unopened part. They told me to courier it back to them and I will receive a full refund within 3 days of delivery. It was delivered to them by The Courier Guy on the 19th of August. I phoned them the next week and they said they will do the refund within 3 days. I did not receive any refund. I have phoned numerous times and get the same answer, or that extension 211 is not available and I left numerous messages with full details, but to NO avail. It seems like they do not want to do the refund. Their feedback is non existent and I am VERY unhappy