Can't change date to December 2018, no Refund and no Voucher option for cancelled flight

We booked a flight for December 2017 early, as this is a very busy time of year, but now our plans have changed. We therefore need to cancel or change the date on the booking. I was however shocked to see that a) a refund was not possible, B) a voucher is not an option, and c) we cannot book for December 2018. Multiple email addresses for Kulula don't work (bounce back) - ********** ********** and ********** which is surprising for a company that prides itself on customer service.