R.K.
Keep calling the postal inspector. I would also contact yor local Senators and Congressmen. The Postal Service is a federal job, these people need to be talked to by someone who have the ability to fire them.
I had an issue with our State Job Service many years ago. A couple of months later my State Senator was doing a radio talk show. I called him while on the air and told him what happened, he got so angry, he took me off the air and got my personal contact info and called me the next day. When I told him who the person was, he personally went to the office and fired her.