Ignoring request for a refund

I purchased a Groupon Voucher but have decided to cancel and request a refund. I requested the refund on the same day via email and have not received a response. I tried phoning the call centre but there has been no response for the last week. There is no alternative number to contact them. Several more emails requesting a response have gone unanswered. Groupon has a clear cancellation policy in place on the website but it is clearly just for show as no one enforces it. I am baffled by the complete lack of service. It's very convenient to state you have cancellation policy but then provide contact details that don't work!