This is the 4th call I have received from the SSI number in 3 days. There is no one on the other end. This is why I registered on the Do Not Call list.
Caller ID said SSI, number = 1-724-252-2526. It rang twice, I answered, but the line sounded like it was absolutely dead. I believe it was a robo-call autodialer. They typically call, and when the person answers, the line sounds absolutely dead as the dialer waits for the caller to say "Hello," then it connects to a human for the sales pitch, but that didn't happen (I didn't get a human at all). Other sites say it was a survey. I have entered them on my call block list. Be aware there is something called "Caller ID spoofing," a technique in which the caller can make the phone number and name that is displayed read just about anything they want it to read.
I too have received several calls from this and other numbers that display as "SSI". After a very quick search, Learned that the company is a legitimate company collecting data for market research. Their website is www(dot)surveysampling(dot)com. And they have a page explaining why you may receive calls from them, even if youare on the "do not call list". Additionally they give instructions to opt out of future calls. I am not in any way affiliated with SSI or any other telephone related business. I'm just someone who used Google, found info which I believe to be accurate at this time, and shared it here for those that do not understand how to use search engines.