Advice - Plain Green Loans

I need some advice regarding a matter. During a serious financial problem, I was forced to take out a loan with Plain green loans in 2017. I know the fault lies with me. The amount of the loan was $1500. However, after learning that tribal lending is illegal I revoked their ACH authorizations. However, by this time I have already paid $3300. Plain green contacted me saying that I still owe them $2800. After saying that they are illegal, I asked for a refund. They didn’t reply me back. After several unsuccessful email communications, I complained about them in BBB. Today they replied me back that they have sold my account to Rocky Mountain Capital Management, LLC on 12/04/2018. As of now Rocky Mountain Capital Management, LLC has not contacted me but they are reporting it to my TU credit Report. Can anybody give me some advice about how to handle the situation. Thank you all in advance.