Miniature Doberman Pinscher Help!?

HELP! My neighbors just gave me miniature doberman pinscher out of no where and took off. The dog appears to be about a year old. I was happy because i live alone and i thought that a dog would be a great companion. (this is not my 1st time having a dog) Well ive had the dog for over 4-5months now and he is not housebroken. The dog is very scared of me and everyone. If You walk or make any sudden move or noise the dog will run. it is almost impossible to pet it. This makes me believe that the dog was abused. The dog continues to use the bathroom in the house after being let outside SEVERAL times a day. When i put the dog in his cage he uses the bathroom in it as if he hasnt been out in hours. He also continues to tear alot of household items up. I dont know how to discipline the dog because he is so small. I Tried to show him what he did wrong but when i grab him by the collar he goes crazy and wont stop moving and scratches me. Pls help me. If this dog continues i will have no choice but to give him up :( Help!