The blocking doesn't work because these are computer generated spam calls (thus how they're able to call multiple times from the same number even while the previous call is still ringing.) Every rare once in awhile it will leave a voicemail (Must be a glitch when they do because they are "interactive" messages that won't work from a VM). Every one of the VM's left are always the same message, one with a male voice and one with a female voice. Once that barrage of calls ends, the next round will be from a new bogus number. There's no reason to even block, as I don't think I've ever seen the same number twice after however many calls they make from one number all at once. With computer-generated numbers through internet calling, the only limit to the numbers is the mathematical combination limit of area codes, prefixes and last four digits, they don't need the phone company to assign them numbers like you or I would if we were to establish a new landline or even cell phone service. The way I understand, the computer generates a number that it has checked to not be in use elsewhere, and makes all the calls to it's list of targets, and then repeats the process again, generating a new number for use. They are also able to generate area codes that don't exist, and are able to generate numbers from your local area code and even prefix to try to get you to answer thinking it might be a doctor's office or some other place of business with multiple phone lines that you may not have in your phone for easy recognition. Some of these robot calls are where they are trying to get you to answer to record you saying a few words in order to enter your voice into an AI program that then can produce the fairly new but popular scam where someone calls with a relative's voice saying they've travelled somewhere out of the country and had their credit card stolen and need several thousand dollars wired to their bank account in order to get home, it IS your relative's voice, but put together electronically from a simple "Hello" or "Remove me from your call list" statement... and the bank account obviously is not theirs. The hope is that you cannot reach the relative for proof prior to sending the money out of desperation. Once again, all it takes is one in a thousand to work to be profitable, once these scammers have the computers and software, it costs almost nothing to repeat the scam hundreds of thousands of times, and they don't have to do anything but click a button now and again. 

Before my Dad passed, he got a call from my Nephew who was 25 at the time, saying he'd gotten arrested and needed $5,000 wired somewhere to get bonded out. This was before scams like this were common and on the news, we'd never heard of it then. Dad said it was definitely his voice, but just knew it wasn't legit somehow. Coudn't reach my nephew for about 10 hours, but Dad said he'd just have to sit there if were real lol. This has been 10 years ago, so imagine how advanced that trick has become since then.