Hi Martin, It appears your credit report has few/no tradelines present, so your lender is documenting “soft” tradelines, which are regular bills you pay that don’t report on credit. The $12 shouldn’t be an issue, presuming your landlord doesn’t state the rent was late. You might try asking for payment histories, rather than Letter of Credit Reference, or just mention that you are buying a home and need to document your timely payment history. Hopefully that will solve any miscommunication.
You can also try providing paid utility bills, paid bills for school tuition or childcare, or paid bills for various kinds of insurance, such as health insurance, life insurance, or personal property or auto insurance. The more letters you get showing that you pay your bills on time, the more likely it is your application will be approved.