The extra \n look like they're probably in the "Address of site owner (seller)" parameter within CBSubs > Settings > Display > Invoices. Turn off Joomlas edit by clicking the toggle source or view source parameter or by setting your WYSIWYG editor to None and you should see them more easily. If still can't find them try just resaving to see if that solves it. You can also check the payment slip parameters by editing your offline payment gateway and reviewing the parameters under "Presentation of payment slip".