Nuisance dogs..no mail delivery?

Once again I'm having problems with the same neighbors. This time it's their dogs. I was just notified today by the US Postal service that my mail will not be delivered due to my neighbor's dogs. The mail carriers are afraid of these two dogs, who run loose off leads (against city codes). I live next door, yet these dogs chase the carrier all the way to my house. I have spoken with my neighbors about this, but they could care less... they don't see why it's a big deal because their dogs are big, but friendly. They have informed me that I should deal with the USPS, not them. Honestly these 2 dogs chase everyone or anything that moves. I understand why a carrier would be fearful. A neighbor was bit by one these dogs last year. I've seen them chase the carrier, but I am also afraid to approach them. The police were called once, but the neighbors denied that the dogs were running free. How can I legally resolve this without causing a really big issue( neighbor feud)? Or is a feud just unavoidable? Also, any ideas on how to document this?