Cancellation not processed and no response email

I bought a Groupon voucher on 08.12.2015 and cancelled it on 09.12.2015 by sending an e-mail. I received an automated response telling me that Groupon will get back to me within 2 days. I waited and haven't received feedback on my cancellation. When I try calling them you just get through an operator with no one answering the call. I want my refund as they promise within 7 days cancellation on their voucher.