Sorry to hear what you two went through. I think the fact that the older brother called police is the key here. He was in position to know better than anyone on this thread whether the situation called for police and court intervention. Not only is 13 way too old for any kind of spanking, but any disciplinary system that results in your 17 year old thinking he needs to call police to protect his younger brother from you, is obviously ineffective as well as being way over the line into assault.
Or the 17 year old has just been brain-washed in public school that he should seek out the government to solve all the problems in the world. He'll soon find out that the "system" more closely resembles a meat grinder.