Taco Cabana review: Unethical behaviour

On Saturday 17th about 4:15 my wife and I arrived to the restaurant. When we entered, we saw an employee moving away from the register. Then, we were waiting for around 10 minutes to take our order. Finally, one of employee came after we asked him to help us. Three of them said that they couldn't open the register. After a while, they opened it and they took our order. Our age is around 60 years old, it is very obvious to realize about that (my wife is Irish American and her hair is all white). She ordered a margarita lime and they asked her about her ID. I want to mention that I do not drink alcohol. In front of the register there is a sign that says "If you look less than 40 years old we will ask you for your ID." We told them about the sign in front of the register and the employees said that the manager ordered them to ask ID for everybody. We asked them if we can talk to the manager. The manager came and told us in a very angry tone that everybody needed to show an ID. We told him about the sign in front of the register, and he said that "THE SIGN DOES NOT MATTER, THAT THE SIGN WAS NOTHING THAT IF WE WANTED TO ORDER THE MARGARITA WE NEEDED TO GIVE THEM OUR ID."
Also I noticed before that they scan the ID in the register (computer). One day, I noticed that they took the passport of a lady and put her information in the register. The lady looked on her 50's. We left the restaurant and the manager threatened us.
Also, we noticed other times that the restaurant had flies and the tables were dirty. We needed to clean them before we sat down.
I have been a very good client for you restaurants.

Thank you in advance for all the attention to this matter.