I think all you need to do is cook your peas for a lot longer ! They can (as the others have said) take about an hour to get to the soft stage, but that depends on how fresh they are ! Very old, dried split peas might take a lot longer. I would only add salt at the end of the cooking, when you check for taste, as the meat might be salty in itself. My mother used to make this dish and also add onions, potatoes and grated carrot to bulk it out into a substantial stew..... and it's now one of our favourites (though without the hock).