NEVER answer a phone call (mobile or land line) from a number you do not recognize- if it's important- the CALLER will leave a message. These SCAMMER/SCUMBAGS WILL NEVER LEAVE A MESSAGE
As noted above, you can file complaints with the State Attorney General for you and them as well. But since it is a Energy business obviously, then you can also file a complaint with the PUC as well, and since they are trying to sell you something, then of course you can file complaints with the FTC & FCC as well.