Debit Run Report and Services Manager

We are a South African based internet service provider ??" Connix Internet. We need a small PHP / MySQL program for managing our customers and their services with totals to be billed. Currently we work on an Excel sheet and it just does not work for us anymore as our users are expanding a lot. We have a monthly debit run to submit and services change constantly especially with ADSL usage, upgrading of domain packages etc. You can just imagine what trouble we have to go through every month to get the debit run sorted out and we need this to get more automated.