Now that you have been served with a complaint and summons, you have 20 days to file an answer. You should also be prepared to respond to their requests for discovery, which will be forthcoming.
You should speak to an attorney immediately. If you do nothing, or do not properly answer the complaint or their requests for discovery, they will move for default judgment against you.
My firm represents debtors in your position all over Massachusetts. For a set flat fee, we work to aggressively to put our clients in control of the lawsuit and get them to a place where their case can be either (i) dismissed in its entirety, or (ii) settled for a fraction of the full amount owed.
Please do not hesitate to contact my office if I can be of any further assistance.