Invoice hints and tips

I run a small exterior cleaning company (sole trader) and it’s still in its infancy. I have made a decent start and picked up some nice work from a few holiday letting company’s and some rich homeowners who holiday in the area. I generally invoice my clients. I use an excel template I designed and i think looks quite professional (I can use various graphics programs proficiently  as well). I email the invoices as PDFs with all the job and payment details. 

Right now I have around 1500£ of outstanding invoices from up to 6wks ago and most of the time when I message I get a “sure I will get it paid ASAP” and then they don’t get it done. 

I don't want want to be over the top company with messaging but I need the money way for the numerous bills I have coming out very month. 

* Do you invoices have a message on them about payment time ?

* What kind of messages do you send to companies to chase a payments ? Examples would be appreciated 

* What kind of timeframe for the chase messages ?

Thanks in advance as always

I literally write on bottom of invoices

'Payment within 48hrs where possible is appreciated'

After a week i send a txt/email

'Having just done last weeks accounts, we have noticed that weve still recieved no payment for your clean on 7th july, please find below outstanding balance and bank details incase theyve been lost or misplaced'

If this doesnt work a quick call 3-4 days later normally does the trick

Ithink the key is be polite but not pushy.

I literally write on bottom of invoices

'Payment within 48hrs where possible is appreciated'

After a week i send a txt/email

'Having just done last weeks accounts, we have noticed that weve still recieved no payment for your clean on 7th july, please find below outstanding balance and bank details incase theyve been lost or misplaced'

If this doesnt work a quick call 3-4 days later normally does the trick

Ithink the key is be polite but not pushy.