Got fired for not selling enough cars and not wanting to post on my personal social media

Im beyond devastated, and pretty upset. I worked at a car dealership and have only been hired for just under 3 weeks. Ive been on the floor for 2 weeks. In those 2 weeks, Ive sold 3 cars. I understand that isnt the best, but they told me it would be slow at first. They also said theyre firing me because I dont want to post pictures of myself, my name, and the location of my job on my Facebook. I havent even got my commission for the 3 sales. I dont know what to do anymore. Im upset. Ive never worked a civilian job before as I just came off of active duty (Army)