If you had a romantic or sexual relationship with your "ex-gf," she normally would have obtained a protective order rather than a peace order against you. But whatever such an order might be called, maybe she obtained an extension or a permanent order by convincing the court that you were served when you were not served--although this doesn't happen that much with such orders, since service is normally effectuated by law enforcement officials.
I would say it is more likely--especially in light of the solicitations--that your ex had you charged in a criminal case when she applied for a protective order or peace order.
But you need not speculate as to what happened, since you can easily pay a visit to Maryland Judiciary Case Search online and/or visit the local District Court and inquire what criminal charges or civil cases are pending against you. If you have been charged criminally, you absolutely should obtain competent representation even if you are convinced that the charges are bogus.
You also may want to be a little more careful about making admissions on this web site ("I guess it was annoying of me"), since your ex or someone else may link them back to you and the government could try to use them against you at trial.
You could get up to 90 days in jail for violation of a peace order. Judges tend to be strict when it comes to violations of the orders they put in place, but ultimately it depends on who the judge is and the nature of the violation. I would strongly recommend that you consult with a criminal defense attorney to determine whether you in fact have been charged with a violation and to discuss potential defense. Regarding the advertisements you received, many attorneys subscribe to direct mail advertising providers who monitor court filings and send ads to people who have been charged with something.