I’d chalk it up to experience, you could continue to complain, but they can’t very well change their mind now can they.
Or as jimdubleyou says you could name and shame on social media – but these days big places don’t fear it as much – unless you’ve got thousands of followers or you can somehow make it go ‘viral’.
If if makes you feel any better, 3 weeks ago My Wife, My Son and I went to view a house to rent, it was nearly £1000 a month – so not cheap, and we live in Wales, not London – as we arrived the agent said “just to warn you, this is the first time I’ve seen it”. It was a pit, stank, dirty and frankly a bit of a wreck – 10 mins in and “oww, oww oww” and my Son is coming out in spots from flea bites, we get a reaction to them so we left, took him home, put him in the shower, his clothes straight in the machine, but sure enough 2 days later we’re getting flea bites – it’s taken me ages, but I think I’ve got rid of them now…