Post Office review: Post Office is withholding my mail

The post office is withholding my mail because the next door neighbor is parking there car to close to my mailbox.
I am not even allowed to pick my mail up at the post office. Until I get a PO Box or move my box AGAIN I will not get my mail. I paid $250 for moving my box first. Because it was to low. Then they ask me to move it again because my car was parked to close. So I ask the people whom live behind us if I can park my car on there property. So I did. Now they will not deliver or let me pick it up until I move the box again.
I do not have the money to have someone move it again. They have been withholding my mail for 16 days now. I am a single mother with three kids whom works for the navy and have a second job to make ends meet. And they can not just step out of there vehicle and just drop mail real quick into my box?
Do I have a chance to fight this?