Well mate we Charge late fee on overdue Invoices.
In my experience, adding (or even just reminding the customer you will add) a 15% late fee is enough to make them pay up. Unless they're planning to never renew, in which case you should offer them the chance to cancel (much better than being suspended for non-payment).
Depending on the product, sometimes the late fee can range from 5% to 20%.
Good luck!!