Name that fruit…

Hi,

I am an ex Durbanite & I have been trying to find a particular fruit name. The fruit used to be called “Dutch Apple” – purple /sweet sour with a big hard woody seed. I was advised to try Crab Apple but it did not resemble a Crab Apple. Albert Park in Durban had many of these fruit trees.

I would be grateful if you could help with the name of this fruit

Thanx, Iris