That's an easy one.

Call the postmaster, and ask him or her to contact their Field Maintenance office to get the box replaced.

Don't leave it with a clerk (not knocking clerks, but they have a lot of work to do, sometimes in several offices, and thigns can get lost in the shuffle).

Give the postmaster a week. If there are still no results, as the postmaster for the contact information for the POOM. Again, you're asking for his/her supervisor's contact info, so don't expect a cheery result. If you can get everyone who uses that CBU (cluster box unit) to call the postmaster and if need be the POOM, I'll bet you get results.