Ugh. I bought a Groupon for some yoga classes. The vendor ignored all my emails trying to book, then emailed me after the Groupon expired to say, "Sorry but email me the voucher and you can still use it!", then emailed me right back after I did so to say, "Actually you can't use it because it's expired", then used the info from the voucher to fraudulently tell Groupon I had already used the voucher. Groupon refuses to refund or do anything since according to the vendor I've already taken the classes, even though, you know, I have the emails where the vendor flat out says, "We won't honour the voucher tough luck."
Groupon sucks, seriously. Is there nothing one can do if a vendor refuses to honour the deal then lies that they've already done so?