Baker Nissan North

I received a phone call from the 2nd chance financial department saying I was pre approved for $20,000 so i visit them found the vehicle I desired and was told I needed a co-signer but that was not possible for me. So if I am pre approved Why do I need a co-signer and why was I unable to get financed??? I still dont know because after wasting an entire day I received no definit answer txt and call the fallowing day to find out whats going on still no responce. I would imagine that the sales rep would have at least replied to a txt sometime thurout an entire day but nope instead I am left with 100% nothing and a waste of my time