After calling several times, where the phone would just keep ringing and ringing, I gave up. I even dialed the area code 787 prior to 911 just to see if I can get through to someone. By the way, for those who do not live in PR, you do have to dial 787 (if you're trying to reach someone in the San Juan area) and then the phone number. It was definitely frustrating when you're desperately trying to get help and you just can't seem to reach anyone. I felt so helpless.
To put it lightly, I was also in panic when 911 wasn't answering my call. Luckily, someone helped me flag down a police officer who was on patrol, something which is a common sight throughout the streets of San Juan these days. Nevertheless, I do have the phone number of the local police station programmed into my cell phone now. This was something which the police officer himself suggested I do. If you live in Puerto Rico, I urge you to look up the number to your local police station as well. For those traveling abroad, it'll probably be a good idea to find out what the local emergency numbers are as well, and hope that someone picks up.