If you think you may actually have a chance of convincing him that, no, Wicca is NOT Satanic in nature, I'd suggest having him read this FAQ from Wicca: For the rest of us.
Each of the three main number sections, as well as the unnumbered "How does one become Wiccan?" at the end needs to be clicked individually.
Here are the most relevant parts, copied and shared here for your convenience;
Is this Satanic?
This one is easy. No. We don't even believe in Satan or other inherently evil entity. Good and evil are choices that each of us makes through free will. Each of us has the possibility for both. "Evil" by definition is nasty, cruel and unpleasant, and we certainly would never encourage anyone to behave in such a manner.
Why do people think it is?
This question is quite a bit more complex. For some Christians, all non-Christians (often employing a very narrow definition of Christian) are agents of Satan. Hindus, Buddhists, Muslims, Jews, Atheists, Scientologists, Druids, Wiccans, whatever. There's nothing we can do about that. It is their right to hold that belief. However, there are people who associate Wicca with Satanism even if they don't associate other religions with it, and that deserves more coverage.
Part of it is Wicca's ties with witchcraft. Many Wiccans are also witches, and many people are still using the older definition of witchcraft: follower of Satan or worker of maleficarum. They hear the word witch and they associate bad things with it. They do not understand the modern witches are using a modern definition.
Part of it is appearance. Think of the images Hollywood uses to indicate that viewers are watching a Satanic ritual: robed figures standing within a circle, pentagrams, ritual daggers, candles, incense, and so on. All but the robes are standard pieces of Wiccan ritual, and some Wiccans use robes as well. These images are much older than popular understandings of Wicca, but they are not older than the Golden Dawn, which used all of those elements.