Groupon oversells restaurant on path to bankruptcy

We purchased a voucher for Myoga Restaurant at the Vineyard Hotel on 22 January which is meant to expire in 7 weeks' time on 22 April 2015. When we tried to book for this Sunday, the restaurant told us they were not accepting any more bookings, giving the excuse that Goupon had \oversold"their vouchers. Since this renaging of vouchers must have started within the last 7 weeks"