How to proceed after being threatened and treated poorly by university faculty after reporting physical assault?
There's a lot to parse here, particularly in the lengthy comments section.  The way I see it is you've got two options:

Go outside of the department for help
Avoid these conflicts and finish

It seems apparent that the department is not going to help you through this, since you mention both the Dean and the department chair being involved negatively.  If you opt for number one, you should look for school-wide resources, similar to Title IX coordinators for gender issues.  I'm not aware of this being standardized, so you should look through your university's resources.
I think whether you go with option 1 probably depends on how close you are to finishing.  If you're close, and you've been able to work successfully with your advisor, is it possible to minimize, or even cut, all contact with the rest of the department, and just get your degree?  It's hard to swallow injustice, but from a utilitarian point of view, there may not be much to gain by fighting with the people in charge of the department you're in.  Letting bullying by fellow PhD students go unanswered by simply avoiding them galls me, even, and I'm the one giving the advice!  But you should at least weigh the option when considering what's best for you; fighting racism in your department, or escaping with your PhD.
Of course if you're not close to finishing, option two becomes far less viable.  I'm sorry you're in such a toxic environment, and I hope you can finish your degree successfully despite it.  Perhaps some combination of 1 and 2 is possible - it seems sensible to immediately begin avoiding the sources of conflict in your department, even if you do opt to challenge their behavior at a higher level.