Customers Database

[LiquorGuy via AccessMonster.com]

I am trying to rebuild my database because I encountered a design flaw. Any
advice on how I should structure the database. The background is as follows:
Simple customer database, with acct numbers, and standard customer
information. Monthly orders, different invoice numbers, different product
descriptions. I need to design a simple database where I can append the new
excel spreadsheet to the table monthly which contains all customer
information for that month and accounting can continue to process payments as
they are received. Sometimes there will be duplicate accounts for the next
month. Or they may be new accounts. I want to keep it simple (one table if
possible) so that I can do an append each month. I know it's bad database
design to do that but that's the only way I can maintain the database, unless
someone has a better idea. I also need the database to list the order
history per account number so that accounting can apply payments to each
invoice but clicking on an apply payment button. I have designed all that
already and its function but I now have to redo the design. I hope that was
clear enough.