What state are you in?
You can't stop the lawsuit but you can postpone the trial of the matter unless you pay the alleged debt or negotiate workout agreement with them.
You can file a response - an answer to complaint/summons. File a numeric response to each number allegation in the complaint against you.
If you don't have any experience writing or drafting pleadings - then I would highly suggest that you do retain local counsel. Usually they can write the response in a half hour or so for you.
Attorney
19 years legal practitioner: real estate, collections, estate, civil, business, and criminal law