How good is confidentiality with physical mail forwarding companies?

I want to use a mail forwarding company that can receive mail for me and forward it to whatever address I request. I have already found many places that do this, but I am worried that eventually my stalker would find out that I use this p.o. box, call the p.o. Box staff pretending to be me, and get my real address. Are there tactics and strategies I could use to minimize this risk? Or know a forwarding company that practises strict identity check over the phone/emails? World-wide ok.