I pride myself on being an easygoing client, customer, consumer. But then this morning happened at the Hoboken Post Office and I lost it.

I have a post office box. A few weeks ago they placed an invoice in the box for renewal. For a year it’s $92 and payment is due by April 30. So I wrote a check on April 22 for the full amount and put it in the envelope provided. I then placed it in my mailbox assuming it would be picked up.

When I noticed today that it was still there, I brought it to the customer service window to pay it in person. The very nice woman took it and was in the process of issuing me a receipt when she looked at the check and said, “The price went up.”

Me, incredulous, said, “When?”

“Last week. It’s $96 now.”

I nicely tell her that’s insane and then I quietly requested a manager. When he came out, I calmly explained that I had been invoiced for $92 and was still well within the due date. Thinking he’d laugh and agree how crazy this was, imagine my surprise when he said, “Well, now it’s $96.”

“Let me explain how the world works,” I said, my voice escalating. “You don’t invoice someone one amount and then change it when they’re paying you. It’s not done that way.”

Manager guy then persists, again and again and again, that the fee is now $96. I tell him — loudly and a little out of control, I’m afraid — that it’s unethical and that I know he has the power to accept my check as is, but I thrust $4 at him anyway and demand a receipt. He huffs and puffs and hands me back my dollars.

OK, really?

I had just come from the gym and I went from a Zen place to one where my blood pressure was going through the roof. My spiritual self says I should have behaved better. But the little bad ass that lives inside of me was proud as a peacock.