India Post — Non-Delivery of Registered Post & other letters

I am the Proprietor of INCOSE, having office at 55-33/1,II Floor, 5 Cross, 3 Main, Hanumanthanagar, BANGALORE-560019. My office is working from 10am to 6PM on weekdays (except Sunday and Public Holiday).
I am not receiving letter from postal department properly. Since our office is in II Floor Post Man is not coming to our office. And also he is not taking the letter back, but throwing it on the stairs on the Ground Floor which is open to public. It is right in front of Ganesh Bhavan BMTC Bus stop. I am able to trace some of the letters lately on the road side on the foot path. This is a very care less act. Even registered posts are not delivered properly. They just mark it as 'Door Locked' and send it back. This is not a proper attitude. It is the responsibility of the postal department to deliver the letters properly to the addressee. If they have any problem in delivering letters to us (because of II floor) they have inform us in writing that they are unable to deliver the same. They can send it back to the sender but they cannot through it on the streets. What about registered letter? Even that is not delivered.