Produce Express interview questions

It went well I thought but I was told they'd get back to me either thar same week or the next, well they got back to me the next day with the job offer, I accepted, they said they'd send the acceptance letter Friday through email, they wanted me to start that Saturday I said I need to give my current job 2 weeks and they were fine with that but I still haven't gotten the letter so apprentely I wasted my time going there for nothing when I could have slept longer.