First and foremost, if the lawsuit has actually been filed (it will have a case number ***** it) then you need to be sure to file and serve a timely answer. That's your first step, regardless of any potential for settlement. That way, you won't end up facing a default judgment, no matter what. If you are indeed dealing with an unscrupulous collection company, then it would be a good idea to keep an eye on the electronic court docket to make sure nothing is happening that you aren't aware of. A daily check might seem like overkill, but it's a good practice. You can access your case docket on your county court website using the case number ***** on the first page of your summons.
Also take a look at the first page of the actual complaint. That will probably be a page or two into the packet you received and will be formatted differently than the summons. It's where all of the allegations are listed. At the very top left of the page will be an attorney's name next to a bar number and below that will be a phone number. You can call that phone number and speak with the attorney directly, in most cases. That's the person who has authority to settle the case and will often do so to save the time and energy.
Often times, unfortunately, that "law firm" listed on the complaint is nothing more than a glorified collection agency with an attorney on board somewhere that appears in court and provides some degree of legal authenticity to the company. In cases like this, you will likely be directed to a "case manager" being denied direct access to the attorney. The case manager will also have authority to settle, and any settlement should be in writing, regardless of the person with whom you speak. If you hire an attorney to handle this for you, the attorney will necessarily be able to get through to the opposing side attorney. Hiring an attorney to handle this on your behalf is an option, but is not necessarily needed, particularly if this is a small debt that you can get handled on your own.
In terms of potentially quashing the subpoena because of improper service, that takes a motion that needs to be filed within the time otherwise designated for an answer. If you go this route, you could buy some additional time, but the end result will likely be the same, either way. If you do decide to file/serve a motion to quash, it is recommended that you have an attorney handle this for you, because you could lose the motion if all the particularities are not precisely followed. A good referral source would be your county bar association. There should be no charge for that referral and no charge for the initial consultation with the attorney to whom you are referred. Again, if you go the straightforward route you should be able to settle a small debt on your own without too much effort. Remember, all they want is a cost effective solution.