The exact same thing happens to me. For the last two weeks or so I've been getting a call from this number at least once or twice per day - usually with no response on the other end of the line. This morning was the first time someone spoke when I picked up, asking if I was a sufferer of chronic pain. Now I can officially know to block this number in my phone.
I keep getting calls on my cell phone from 305-203-3981. They have never told me who they are and it's hard to understand what they want because they have really thick accents. I have told them to stop calling me and for them to take me off their call list. They are still calling me multiple times a day. The calls are all 5 - 10 minutes apart between 4 pm and 5 pm. When I call the number back I get a recording saying that the number has been disconnected or is no longer in service. It's gotten really annoying really fast.
Got a call on my cell phone yesterday from FL, USA. Caller left no voice-mail. Since I have no contact in Florida, I marked this number as a "Blocked Contact". Thanks to this post and my iPhone.
Like everyone else, I get called several times a day every day by this number and when I am home and answer the phone, no one says anything. When I call back, I get a busy signal or a message that it is disconnected.