Mail Theft and Tampering in My Building – Need Advice

Hi all, I need help and suggestions.

I recently moved into a new building in Miami. Since then, I’ve had five separate incidents of credit card mail being stolen or tampered with. Here’s what’s happened:

• I’ve filed police reports every time. They told me the reports are for documentation only. No investigation.
• I contacted the U.S. Postmaster and submitted a mail theft report. No answers yet.
• I wrote to my state representative.
• I told building management. They weren’t surprised. They said it’s a known issue. It supposedly started about a year ago when our longtime mailman retired.

Still, it keeps happening. Today again, I had another credit card stolen. I knew it was coming because I use Informed Delivery. All my other mail showed up—except the credit card. In two other ocasions, I received a credit card envelope already opened (I didn't activate it and contacted the bank).

At this point, I can’t safely receive any important mail at my own address. I feel stuck.
I’ve tried everything I can think of. Nobody seems interested in doing anything. It’s a messed up situation.

Has anyone here had a similar experience, especially in Miami? What else can I do?
Should I get a PO box? In a different zip code?
I’d appreciate any advice.