Some former owners in my commercial building sued me for eviction, received a default judgment. What can I do about it?

I leased office space from a corporation in a commercial building. The building was sold at a tax sale in August of 2013. I contacted the new owners who agreed to drop my rent from $750.00 to $500.00. A tenant in the building who used to be part of an ownership group then sued me for eviction under her business name. My lease was clearly not with them. Notice was posted after 10:32 p.m. on January 31, 2017 for a court hearing at 8:30 a.m. the next morning. I arrived at my office at 9:45 a.m. February 1 to find notice posted on the door. I also never received a first class letter as required under the laws of Mississippi. Mail is put in a box outside the building and the tenants who won the default judgment control the only key to the box. I believe what they have done is criminal. Please help me to know what I can do now. They sued me personally, not my business. Thank you.