Customer prepayments

We are a wheelie bin rubbish collection business and we invoice our customers at the end of each month for their bin empties.  Many of these customers make payments in advance of this invoice.  I love MYOB but their prepayment handling is frustratingly time consuming and ineffective.  I have to create a credit note to apply the advanced payment to when if is their first payment.  After their first invoice, I can open up the closed sale and apply the advanced payment to it but it can be a few months before there are sufficient closed sales to do this to because you are not able to apply a payment to a sale that is already in credit through this method (why not I don't know?).  I then have to match off the credits against the invoice - this process is frustrating as the list of credits doesn't tell you whether there are any invoices to match the credits to so you must attempt to process each to find this out.  Finally, the prepaid invoices don't get emailed to the customer because they are zero balance so the customer doesnt get a copy of the invoice (I can't find any way of sending a zero balanc invoice to a customer).  If our business continues to grow I am going to have to ditch MYOB in favour of something that is better at handling payments in advance, which will be really sad because I love eveything else about it.  There must be a better way or something coming down the line from MYOB on this one.  Solving even one of these problems would help please?