Here's what I did. I sent the registered mail by going to the Post Office which is assigned to deliver the demand letter in their area. By doing this, I was able to get the return card the very next day. I also gave specific instruction to the mailman to deliver the letter to his house early in the morning since he leaves for work early and letter carriers only deliver mails starting at 10 in the morning. Because of this, I was able to catch him before he leaves his house, otherwise even for the 10th attempt I bet the mail man still wouldn't be able to deliver the letter and have it personally received by him. Once he has signed the return card, I immediately asked the post office to provide me a certification stating that the letter i sent was actually sent to and received by that person personally.
My next step is probably to find a way to make the Post office send a request to NBI to do a handwriting examination to further verify his signature on the return card since I read somewhere that there was one particular case which reached the SC and was dismissed because according to the decision, the signature in the return card must be authenticated. The only problem is, normally, NBI only accepts requests coming from the court, prosecutor, or a government entity. I'll try my luck with the postmaster and see if i will be able to convince him.