It's called 'caller id spoofing'. The people calling you can make any phone number show up on your caller id. They're making a number show up that charges you money if you call it and press a certain key.
At the same time they've disguised the messages on their pay by phone system as surveys. Those messages normally tell you what you're buying and how much it costs.
Check your bill for unwanted charges if you called this number back.
Same thing. The amount of these calls are increasing and now arriving from multiple numbers. I'm not sure of the purpose or intent of the call in the first place. You would think they'd try to sell me something, try to deceive me into giving away millions. But, no they'd rather spend thousands in cell phone minutes annoying the crud out of tens of thousands of people.