British Airways Delay causing me to pay double for tickets

I was travelling from Iceland to Skukuza, South Africa, with stops in Heathrow and Johannesburg. My flight BAoo55 in Heathrow was delayed for over two hours, due to maintenance/repairs to the aircraft. This delay resulted in me missing my flight from Johannesburg to Skukuza. British Airways did not provide me with a new ticket to get to Skukuza - even thought it was all one booking. I had to purchase a new ticket for a later flight to Skukuza. I do not understand why I am being penalised like this if the delay was out of my control. British Airways should reimburse me, it is their fault that I missed my flight. I emailed them, but no assistance or response.