Verizon won't accept calls from a specific business even if numbers are unblocked.

I work consistently will a local business and all calls from their land line phones  to my cell phone are automatically blocked even if I've unblocked specific numbers. At first it was just me but now it is many folks who use Verizon as a carrier. I've spent hours on the phone with both Verizon and Apple to try and resolve with zero success. Incredibly frustrating!