Sorry to hear of your experience. I too have been through the grinder with them. Not knowing all the facts of your problem with UPS, I can only make a few suggestions.
You may qualify under the 1993 Family and Medical Leave Act. Even though you did not request it, UPS is obligated under the law to be aware of people who may qualify under the law. If you do qualify ,then your job is protected. You may also qualify under the Americans with Disabilities Act. My best suggestion is to get copies of the laws(you can download the laws in their entirety from GPO.gov., or DOL.gov.) In case you don't already have a lawyer , I used (removed by webmaster, no advertising on this board please.) This is his field of expertise.
I know how they can grind you down. I was fired on a trumped up charge, did get my job back, and eventually the management person that was behind my harrassment was given the option to resign or be fired, due to several people he had been messing with.
Good luck to you. Keep fighting them, eventually it gets to someone higher up, and things get cleared up.