How to handle bullying at a new job?

I started a new job a couple of months ago. The employees in my department are also new and know each other personally. I’ve noticed the group purposely excludes me and does not inform me of any department news. Most of the employees are nice to my face, some are blatantly rude. They tend to demean any work I do. I have spoken with my supervisors who do not handle the problem. Instead, they go back to this group and tell them that I had come to them with an issue. I have tried speaking to these employees directly which has been unsuccessful. Today, my co worker left her email open and I saw that she has been communicating with the others, each saying terrible things about me. I have about had it. I like my job, but this group of employees which make up my department will not give me a break. I also feel that they could damage my reputation. Do you have recommendations on how to remedy this?