A monthly reminder for a person is great. A monthly reminder within a business organization is what? A calendar event for everyone in IT? For the whole company? The nice thing about monthly billing is it comes from the outside and would get bounced around until it found the right desk.

There are plenty of outside reminder services that send reminder emails. Are you saying that the company has a physical address it will always answer but not an email address? Or that it will ignore regular emails to this address unless they contain a bill? (If bills do get reliably paid, why not just make them every 10 years?)