They left a message saying "Save 15% on your Com-Ed bill"

Utility scam. Do not give them your account number, even to compare rates. They will enroll you and it will take time and money for you to go back to ComEd. Beware...these scumbags operate with complete freedom to steal...if they called you with this number, they will call you for the rest of forever with ever-changing numbers. No one has time to prosecute them, so its up to you to not answer or hang up if you mistake the caller for a non-criminal.

called said he was from ComEd and said that  I could eligible for a discount on my electric bill if I paid my bill every month and asked for my zip-code and asked me to get a copy of my bill and give him the account number.  I told him I didn't have time and hung-up.  He spoke with a very thick Asian accent..

Unknown number - blocked