Ask a career counselor for answers ASAP
With a job such as yours which needs accuracy as well as being professional to customers and staff, what you have been dealing with is amazing in terms of abuse from co-workers that are not at the same level as you. Nothing you are dealing with should be allowed at anytime. The abuse that is going on does not show well to the company as well as the customers that might hear what is going on.
You have done everything required as going up the right channels with HR. It seems that HR is going with the company line and not backing up their employees which can be common with a large firm. A thought is to possibly speak to those higher up in the chain of command as you have talked with HR with no results given. Sending a message to those in charge might help in getting HR to take a better look.
I am sure you are not interested in looking for a new job but this might be something to consider if nothing is going to be fixed in terms of having co-workers act in a more professional manner. Your field has growth potential so I would believe that another position with another company might be the way to go. I might also suggest that to see if a transfer can be made to another office that can get you out of this bad situation.
I hope that the information provided has been found helpful. Also if you could please take a second to rate my assistance so that I know my help was found useful.