we don't know the cost basis either. contact the broker. you should have received a 1099-B regardless of whether it shows the cost or not.
Why didn't you get a 1099-B? Your broker is REQUIRED to provide that. But, depending on when you bought the stock, they may not be required to provide you your cost basis. That's your responsibility to keep track of that.
Unknown cost basis
You have to report the sale on your tax return. Lacking any cost basis, the IRS will consider the entire sale amount as taxable. So, you need to make your best effort to determine the original cost basis, even if (worst case) it's a guess. Historical prices of publicly traded stocks are readily available on the internet and should, at least, satisfy the IRS that your basis wasn't zero; just "google" “Historical Stock Prices". I use http://bigcharts.marketwatch.com/historical/. The stockholder relations dept. at Duke Energy may be able to help.
Even if you did not use a broker, and sold it directly thru DUKE, they had to send you the proper form ... contact them to get the form if needed. Otherwise you can simply enter the sale without the 1099-B form however you will need to figure the basis on your own.