Billing Management System

I need a billing management system to replace the system we currently use.? It is very outdated and hard to use.? We currently track about 8000 accounts on the system.? The system needs to be able to calculate charges including an interest percentage every month. We also need to be able to run several reports (Approx 15 reports) We also have an online reporting system that would be ideal if this software can link to it automatically.? Please send me details and I will contact you? to discuss the program and show you what i currently use.? I prefer someone that can talk on the phone as it is easier for me to relay my requirements and thoughts in that manner, I will then post them here for you to bid on.