The owner of a Gainesville clinic that closed suddenly in August has agreed to pay $20 million to settle claims that he billed for services he didn’t perform and unnecessary diagnostic tests. Dr. Robert Windsor owned the Georgia Pain Physicians office on Queen City Parkway, which closed without notice a few months after he pleaded guilty to the allegations in March. Windsor will sell all but one of his residential and commercial properties, plus two boats and four personal watercraft, giving those proceeds to the government as part of the settlement, according to authorities.