In the past I have gotten hold of the manager of the sorting office responsible for delivery to this area. Speaking to them personally I found that they took onboard all my complaints and I did find that my service had improved. If your about during the day you could try and catch the postman himself. We often have the same chap who calls between 11 and 1. Unfortunately parcel delivery is an all together different matter and for that I can offer no advice.
All the best