What is the US phone number for the Grupo Senda bus company?

I am taking a bus from Atlanta, GA to Mexico City and after doing research, I have decided to take the Grupo Senda. I was able to find their website and I am able to make a reservation but I have no idea where to go to catch the bus or any other details of the trip. It gives me the itinerary but that's it. I would like to know if anyone has a phone number that can be dialed from a US phone or if anyone knows where I can go in Atlanta to speak with someone face to face. Please, also provide any additional information that you think I should know about this company, or the journey to Mexico City. Thanks for all of your help.