After my mother retired to another country she left a rose plant in the back yard, and since we are remodeling the backyard I decided to try to help the lil guy out. When I first got to it it had black stops on 90% of the leaves and in some stems. So me not knowing anything about gardening hit google up for some tips, they said to cut off all of the leaves and stems with black spots, so I did. Which was a lot, I thought for sure this plant if going to die. So I watered it and 2 days later now the plant has white spots all over and the roses and slowly dying off. I also changed the dry old soil to some potting soil. I read that the spots were a fungus and that I should spray a mixture of baking soda, oil, wated, and dishwashing soap. I spayed if once with that, not sure how many times I should use it. Can anybody help me? or have any tips or maybe tell me wth this plant is inflicted with. Should I scrap if?

(dont have any before pictures)