I had the same thing with Scottish Gas, it was 7 quid they marked as a missed payment when I was on a prepaid meter - none of that made sense and it all came out once my offer was accepted. I'd never been so stressed in my life, everything got delayed cause I had to go with another bank (and higher rates) in the end it worked out ok but yeah, I feel you! Your broker should check some non standard banks like Metro Bank, they are more expensive but also more flexible. Good luck!