They did that to me when I was fresh out of high school . Did some js/html fixes for a few days for some guy and got $200. A few weeks later, original hirer charges back Upwork (I contacted him and he told me it was a different work that wasn't delivered by the other person). Upwork goes into damage control and sweeps my entire balance and tells me it is part of their policy. They claimed they would return it if they won the charge back claim.
Never went back.