Please go to the "Payments" section in your customer area and click on the "My balance" window. Here you will find the open invoices for this month and the options to top up.
You can top up your customer account by QR invoice or by manually entering your bank details in your bank's online banking.
In case of QR invoice, your reference number will be transferred automatically. If you enter the bank details manually, you must also enter them so that the credit can be posted to your account.
If you do not use online banking, you can order payment slips that can be used at the bank counter for topping up.
Click on the following link for a further instruction explaining the "My Balance" field: How does the "My Balance" field work?