When they deliver, the person who sign off will have to give their full name and IC. Poslaju will have that person's IC and name.
Call up Poslaju, ask what happen and make a report with them to investigate.

Do you live alone? If not, check with someone in your house whether they sign off anything.

Check with your sender whether it was the correct address or not. He/She should have the receipt and it should have the recipient address there. Try to find out who's at wrong here.

By right, the Ahmed guy shouldn't accept it. If the person claims that he doesn't know the recipient name on the form, then Poslaju will send it back to the sender.

Then again, we live in a society where people are greedy and can't be trusted.