Caller keeps calling and hangs up after I answer

the number is 121-761-74758

Anyone know who or what this is?
I received two calls in 2 hours from this number and when I answer, there is no response.  The first call had an ID of "V32814555600015".

They called me at least half a dozen times already today also. I did answer a couple of times and only once was there someone on the line. The guy said he was from Liberty something-or-other and asked if I had had an energy credit applied for my electric service. I said I wasn't interested and hung up. They have called back at least 4 times since then and no one is there. VERY annoying!!  I am assuming that this has something to do with the recent vote to allow folks to buy their electric service from companies other than Ameren.

This number has called me 5 times already today. I don't know who it is so I haven't answered.