DS (9) attends a club. Fees are paid monthly, in advance and vary depending on how many clubs occur during that month. They don't operate on school holidays but also follow a different schedule of holidays to our school (for example no club this week even though school started today) - club is not associated to any school.
I pay my fees as soon as the invoice arrives in my inbox, as in within minutes. Today I received an email from the club advising that they expect me to pay on the first of the month and not when I receive the email. My issue with that is it can be hard to work out how much I owe every month. They don't accept annualized payment (e.g equal payments each month). Some months I've paid £96, £124, £132 or £144 so it's not straightforward.
AIBU or are they?