Billing from nursery’s was like some sort of mystical art. We did the same number of hours each month and every month the amount came out differently! The explanations were always bonkers!
problem is good nurseries are hard to come by and they k ow that you will be loathed to mchange if your kids are settled, or that they have a waitlist so don’t care if you leave or stay.
its shocking customer service and in any other situation most people (because this post shows me that clearly it’s not all!!!) would be cross about it. Communication from nurseries is key but they can often be so blooming awful at it.
i guess you have a few options. If the activity is normally paid dec - Feb, I would be tempted to wait to the final payment in Feb and not pay it. I would also email your complaint to them and explain this wanting an explanation. Having it in writing is always best because I also found that staff would unexpectedly have amnesia about conversations.
alternatively don’t pay December, but they then may prevent your children from doing the activity.
clearly looking for a new place is an option but I imagine locally that will be challenging (and they know it)
or, sadly, suck it up reframe it as a Christmas present and don’t get the staff anything next month.
sadly they often have the upper hand in these situations.