AITA for charging for a service that I did not provide?

I babysit 3 kids (3f, 5m, 8f) semi regularly. Last month the mom texted me and asked if I could drive the kids to school/daycare, pick them up, and babysit for 3 hours after for all of last week. I said yes and told her how much I’d charge for the week. She agreed then told me her husbands work schedule changed and they only needed me Wednesday-Friday. I adjusted my price and she paid in advance.

Wednesday I get to their house at 7:30 to get the car/booster seats and to drive the kids to school. Their dad gave me the car seats and told me they don’t need me to drive the kids to school at all this week. Then he asked if I could deduct that from my price and pay it back to them.

I told him no. I was not told that I would not be driving them to school until the day of so they will not be refunded. Then on Saturday he sent me a venmo request for what he thinks I owe them. I didn’t pay him and he got my mom involved (they’re my mom’s friends).

My mom thinks I need to pay them back because I’m charging for a service I did not provide but I think if they didn’t make it clear that I would not be driving them to school when they already changed the schedule that’s on them.

AITA for charging for a service I didn’t provide?