Account is in a mess

Good Day<br> <br> My account is once again in a mess<br> <br> Please tell me something. R 1326.34 + R 388.71+R299.00 = 2014.05 which is payable by the 30th of this month<br> Now on the 11th Nov 2015 I paid R 1326.99 which supposed to leave a balance of R 687.09 which is payable at month end<br> <br> Where do you guys get R 1271.76????? Please fix this once gain<br> <br> You got credits on this account for what I don't know and you not matching it up to the right invoices.