Trainline Review - Poor Service And Uncomfortable Journey

I've never encountered a company as bad as Trainline. The cleanliness and control are truly terrible. When I boarded the train from Leeds to Manchester Piccadilly, I found someone else sitting in the seat I purchased. As I explored other carriages, I saw that all seats were occupied. Why can't I sit in the seat I bought, and why aren't these checks being made by the staff? The ventilation on the train was poor, and the smell of sweat was prevalent. Additionally, the toilets were truly awful. I had to stand with my backpack for an hour and a half. I complained to customer service, but there was no follow-up. At the very least, I expect a refund.