Flight cancelled & airline not responsible

I bought a ticket for a return trip from Johannesburg to Bulawayo for a funeral. Departure was scheduled for Friday 15 May at 12noon. Got to the airport at 1015hrs to check in, only to be told that the flight had been cancelled due to technical issues. I asked what arrangements had the airline made for passengers and was told that I should come back the following day for \Re-accommodation". I explained that I could not wait for the following day and would therefore require refund to book with another airline. I was informed that FlyAfrica does not do refunds but will get a voucher that I can use within 3 months. What if I have no intention of going to Bulawayo within those 3 months - there was nothing that the airline can do. I travelled on Zimbabwe's national airline and returned yesterday (Sunday 17 May) and lodged complaint and request for refund from this FlyAfrica .Received an e-mail informing me that the carrier has no contractual obligation to me and that the fare that I have purchased in non-refundable. They then quoted the fact that they follow the Warsaw/Montreal convention which when I read it clearly states the opposite of what they are saying. I want my money back. """