I hear ya...sounds frustrating....
I have a PMB not a POB which just means it is something I pay for at Mail Box Etc or Postnet. For whatever reason P.O. boxes have gotten a bad rap in business the past decade. PMBs or Personal Mail Boxes seem to still be acceptable. I think they cost about the same, not sure if that might be an option for you
Other thing is if you really want to participate in an offer - send an e-mail through the contact button saying what you just did above. It's a reasonable explanation and I'll bet most companies would accomodate you.