Summary of cost for Date Ranges by Month/year

Hi guys,

i have attached the spreadsheet

basically I am trying to total this spreadsheet up to work out a sum for the month by customer number.
some customers made a payment in jan 2012 and paid again in jan 2013, some paid twice in one month.

what needs to happen is

it needs to have customer number going down and the month/year going across the top with a summary paid for that month

i have attached the spreadsheet.

can anyone help?