It's HeyCosmo. Some of their services sound useful but others (like prankster) are not ones I would like to receive a call from. And their business practices are sneaky (see below).
Apparently, if you call this number back, you will hear an option to block your number. Instead, I blocked mine using their web site. Either way, if they ask you whether you are calling from a cell phone or whether your phone is capable of receiving a text message, RESPOND NO or you will start receiving text message spam.
To block HeyCosmo calls using their web site, you must have your phone handy. Visit www.heycosmo.com. Click Block/Unblock and enter your number. You will receive a phone call on that number a few seconds later. Follow instructions. You will have to press various digits. After each press, listen immediately for the next instruction. REMEMBER: When it asks you if your number is a cell/mobile phone, RESPOND NO or you will start receiving text message spam.
If you do receive text message spam, call the number in the text message and opt out. You may still receive spam every few minutes for up to 24 hours after you opt out. I turned off my text message ring tone during that 24 hours.