Got this fixed already. I brought my car to a local door lock/wiper/power lock repair shop. First idea on my mind was to ask the repairman to transfer the lock cylinder of my passenger's side to my driver's side then have the door latch replaced with a latch for the rear door so I will have only 1 key lock. After explaining what I wanted to do, the repairman suggested that we just replace the lock cylinder. He offered initially 650 pesos but I was able to haggle it to 600. Realizing that 600 can be worth it rather than looking for other options. He had it dismantled, and with our surprise, we found out that the lock cylinder does not have any teeth anymore. That was the reason why any key, or even any hard stuff that can fit into the cylinder can open the door. He got a lock cylinder from a surplus door latch then had it calibrated with my car key. That fixed the problem.