I want blizzard to answer this question.
Unfortunately, all you can do is report and raise awareness in the matter, I had one this evening, as frustrating it is, you just got to report the culprit and move on either to the next game or until the next time you attempt the next round.
its happening in every game above 3k cr i have lost my r1 beacause they want me to pay to keep it. I have lost over 100 cr now, every game i play its lost to due of wintrading. Same players doing it over and over and nothing is happening