GSM Automotive interview questions

I went to Witney site for an in person Interview . Since the HR was not there so another person with a lot of work ex interviewed. He considered me suitable for the role and then offered me the job at last. He told me to resign from my previous employer and serve the notice period . He also told to let me know the start date the next day at the earliest possible. I did the same and I resigned from my previous company. He called me and said that after my background checkhe could not hire me . I was in shock since I had applied for the resignation already and that was my only hope. He first said that your visa has issues and I clarified that it is a post study work visa which allowed me to work full time and I sent him the proof also. He then came up with another excuses and did not give me the offer letter at last. I was devastated because of this unprofessional behaviour from an experienced employee of such a big firm . It will take some time for me to digest that I did not make it. The interview cost me around 12 hours of travel and lots of money and most importantly my mental health.