WA Commonwealth Bank sold my debt even though in debt agreement

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12 November 2019
I had a personal loan with commonwealth bank as well as a couple other debts. I entered a debt agreement end of last month that commonwealth bank voted yes to, and then I get a letter stating as of 5 days after the beginning of said debt agreement they have on sold my debt to a collection agency. Is this legal considering the debt agreement is part of the bankruptcy act, and the amount they are trying to claim is higher than that on the debt agreement?
I can't imagine why they'd sell the debt if they'd agreed to the Part IX Debt Agreement?
Do you have any paperwork on it?