While I agree with all the above to a degree.
To some degree, you just need to suck it up if you want to keep cleaning for them.
One off-no problem, debt letter, court action, debt collectors etc etc.
But if you want to keep working for them then that may stop you getting any further work.
In business you'll always have a 'rolling debt' IME.
The bigger the jobs you do-the bigger the debt overall.
I find that most people are quick to mention negatives like you have in starting this post but few praise the quick payers cause it's what we expect.
The majority of lads on here (certainly ones I know) have the rolling debt but sooner or later it does roll in.
In the grand scheme-very few companies will screw you over.
The ones that will-You'd've probably had a guy feeling they would anyway.
Try not to worry. It'll come in, eventually.
And next time you do the job, if there is a next time, just realise that they ain't gonna pay straight away.
And finally-someone I know sends invoices like so:
(For a £100 job)
Invoice due: £110.00
If payment received before xx/xx/xxxx (14 days) reduced price of £100 due.
I've not done it, but it works for him.
All the best.