Yes it is the World Wildlife Fund, and they periodically make unsolicited daily calls that can last up to several weeks. This happened to us several times and we finally decided to stop supporting WWF. It's a shame that an organization dedicated to a good cause resorts to unethical fundraising tactics which alienates people.
Received several calls in the past couple of weeks from WWF, World Wildlife Fund, but didn't answer the phone. They never left a message. Called the number back in the evening, and a recorded message said it was after their usual business hours, so I left a message for them to remove our phone number from their calling list. Hopefully, the calls will stop.