right, here goes my issue

I have been cleaning windows for a management company for a few years, they pay me what i want but take ages to pay, 30 days from when they receive the invoice till they look at it, then another 30 days after that till payment, i accept this, its not great, but hey ho

anyways, they asked me to clean some flats in Oxford, its a good 90 mins drive away, so i said it was too far to clean these 3 windows ( i used google street view to look at the job ), they insisted, they know i will do them when i say i will etc etc, so the 3 windows started of at 3-4 hours travel time and £30 in fuel, so i gave them my daily rate and added a little on, just to put them of, i did not hear anything about it for a while, then a contract arrived for the job

I invoice them every other clean ( so every 6 months ), which in hindsight is foolish, i will change that to every time now

so i have cleaned them in July and Oct, i sent the invoice when i got back from Holidays in Nov with a stack of other invoices for other jobs i do for them, they were all paid at the start of Jan, all except this one, So I e.mailed to ask why, they replied to me yesterday ( after I had cleaned the site again for the Jan clean )

It turns out the management company had lost the site last summer, so I have cleaned them 3 times in total after they had lost the site

Now personally i feel the old management company should pay

BUT

the payments always came out of the " residents board account " so the old management company have said i will just need to invoice the new company and they will pay as the payment will come from that account

who legally will need to pay me ? ? ? if its the old lot, i will have to tread carefully as i wouldnt want to drop the property agent in it, as it is only £ 750 and the work i do for them per year means i wouldnt want to upset them and lost all the other work