OK, so the debt is now owned by a third party, which does put them into the definition of debt collector. However, the attorney does not fall under that definition. Mass law defines these parties in Section 24 of Title 15, Chapter 93 of Massachusetts General Laws.
So your question is whether or not they are required to follow the collection laws of your state and the FDCPA if it is a business debt, correct? If that is your question, and based on the facts you've given (that you were operating under your own name with a d/b/a), it does not appear to have a bearing on this matter as you are personally liable for the debt - so any collection action against you would be regulated under state law and FDCPA regarding consumers - because you are a consumer. The qualification is not the type of debt, I get that the debt is business debt, but the type of borrower.
If you believe you have a defense to the collection of the debt, I encourage you to consult with an attorney licensed in your state who is familiar with Fair Debt Collection practice and potentially debt settlement.
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Thank you for the opportunity to assist you. Best of luck to you!