It took me almost 4 months, but he eventually came around. I don't know how extreme your case is, but it sounds very much like my Leo. It hurt my heart to see him so afraid of me even when I said no to let him know he was doing something wrong.
I could use the loud no because he was so afraid so when he was doing something wrong I would get a squeak toy to distract him and move him when he wanted to chew on something. I did the same thing when he was peeing or pooping where he was assigned. I would keep him close to me at all times because he couldn't handle being in a cage for even a minute without freaking out. Just a squeak toy to distract him and move him to his pad and it took patience but he got the hang of it
I have no advice about grooming, but my shih tzu was terrified of ppl and I worked hard on him accepting other ppl....but grooming is something that I have to do for myself. On the bright side he is the most amazing dog when it comes to other animals. He has never met a creature that he didn't love and want to play with.
Best of luck with your puppy