My question involves a fine from the state of: Texas
I am a resident of apartment. I parked my car around 7 PM. Then, the apartment worker came and told me that I was speeding and have to pay fine by tomorrow noon ($50) or $100 after-hand. There is speed limit 10 in the apartment complex, but I never remember speeding that high. When I asked him proof, he said that he measured using his eye. When I asked other evidence such as speed radar gun, he said that his eye was accurate (When I asked him how high, he said it was 20 mph). So when I argued that eyewitness is not proper evidence based on traffic law, he stated because it is private property, apartment management can do whatever they want and threatened me that he will tow away my car tomorrow morning. So when I asked him how I should pay fine, he said that I have to pay $50 at apartment by noon or otherwise $100. He also informed me that there was notice sent 6 weeks ago, but I never got such notice from my apartment. When I told him that I don't have money to pay fine as I am poor student, he took the picture of my car plate and threatened me again by saying that I cannot get away from this case. Is it even legal that apartment worker gives you fine with threatening like this? I am planning to talk to apartment manager tomorrow, but if they say that I have to pay fine, what action can I take to fight against this case?

