Our school allow our 8 year old to walk home without being collected but we had to write a letter confirming that (again short walk no major roads and we have confidence that she can accomplish this safely/she is happy to do so & normally goes with friend who lives on our street).
It's not about being too lazy to collect it's about assisting your children to develop their independence - parents should be able to judge what's appropriate for their own children.
Send them something like:
I am writing to clarify my expectations regarding my daughter, and her ability to walk home from school on her own. After careful consideration, I have determined that daughter is responsible and capable of managing the journey home independently. As her parent, I am confident in her ability to do so safely, and I formally request that she be allowed to leave school at the end of the day without the need to be collected by an adult.
I recognise that the school has its own policies, but as her parent, I am the one who ultimately decides what is best for my child. Therefore, I expect my decision to be respected. If there are any specific concerns regarding this arrangement, I am open to discussing them, but I want to make it clear that my decision on this matter is final.
Furthermore, I have been made aware that daughter has been placed in the after-school club without my consent, and I have been expected to cover the associated costs. To avoid any confusion, I want to be very clear: I have not requested or authorised her participation in the after-school club, and I will not be responsible for any charges related to this.
If you should call again asking me to collect her, I will simply be reminding you of my decision. I would appreciate it if you did not delay her departure, as it is preferable for her to be walking home at the normal time and not later in the evening."
There will likely be a couple of stand offs- just firmly polite over the phone - I'm not sure why we're having this conversation again, she's to walk home. If they're so aggrieved they'll make a safeguarding report but that wouldn't come to anything if it's as you've described.