I am so sorry this happened to you! Sometimes, we do learn the hard way. Marble is not a very tough stone, and anything abrasive probably will scratch it. A lot of people on this site seem to think baking soda is God's Gift for Cleaning. I dont. I think it is too harsh for many surfaces, plus frankly, it isnt all that cheap. A while back, I picked up a new customer (for house cleaning)./ She had hardwood floors, very beautiful floors. Her kids had spilled something sticky on her floor, and she used baking soda to clean it up. Well, it worked but it left serious scratches all over the floor. She had to replace those hardwood planks....not inexpensive!
Good luck with your marble, and let us know how you make out.