Office service provider seeks software for dunning process

We are an office service provider (invoicing, paperwork, accounting, etc.) based in northern Germany and are looking for software for our dunning process. We operate nationwide. We generate fewer than 500 reminders per year.

The software should meet the following requirements:

• Reminder functions
• Create reminders, including for customers
• Monitor deadlines and due dates
• Open item management – nice to have
• Installment payments – nice to have
• Interface to existing law firm software for tax advisors, if necessary
• Multi-client capable
• On-premises or web-based
• Suitable for home office – would be ideal

Four software workstations are planned. We work with MS Windows systems.