Unfortunately it appears that because the various alternative energy suppliers for your gas or electricity distribution company are considered business partners and you have a business relationship with the distributor, their calls are permitted under the Do Not Call regulation sad as that is. However they are supposed to place you on their internal Do Not Call list same as any other company you do business with is required to do if you request it.
Update:
They have called under telephone numbers: two calls from 860-761-9967, caller ID displays of "Energy" one time and " V6251107340004942724" the other; one call from 860-761-9968, caller ID display of "V6151050530004942724" and three calls form 860-761-9969, caller ID displays of "V6102003250004942724", "V6081040330004942724" and the third time Caller ID was blank.
As I "blacklist" one number, they roll over to the next. They've called at least six times between June 8, 2013 and today, June 25th.
I don't know if they're related but I've also received calls from (203) 538-0974, caller ID displayed "V61812193600049" , and from
(203) 538-0972, caller ID displayed " V61214225800049".