Flight delay without advanced notice

On Friday 14th June my family and I booked a British Airways flight from JHB to DBN to attend a family funeral. Upon arriving at the counter to check in our bags we were told that our flight was delayed by two and a half hours meaning that we would not make it to DBN in time. I find it unacceptable that we were only informed of the delay at the check in counter as we ended up wasting three hours at the airport - time which was taken away from work and family. We were told that we would be compensated for the delay in the form of a free flight voucher, however we have not received any information from the airline.