Groupon converts Money to useless Groupon Credit

Groupon sold vouchers for a shop that during the entire time of their promotion did not have the product in stock that they advertised and when they finally folded (went out of business) groupon converted the value of the voucher back to Groupon Credit. I want my money back... not some useless credit. I want to be able to spend my money wherever I want to. I have made 3 calls to them regarding this and sent multiple emails without any reply from them... today their call centre is closed for maintenance - how long before they also go out of business and my Groupon Credit is worth even less than it is now???