Lock Down

My computer went under lock down as soon as I tried opening the Internet. I didn’t know what to do because I’ve never had a virus and I do not work well with computers. It asked for my credit card number so I put it in and everything went back to normal. Then a few days after the same thing happened. I called my credit card carrier and found out seventy dollars had been removed. Someone talked me through how to remove defense center. I guess that was the problem. Something had took control over the center of my computer.