I've been that parent, kind of,,, in my defence I was in the right though.
One winter, Dd then in y3 came home with someone else's shoes on, no biggie on it's own except they were four sizes two small (.same style though) and her toes and heels had blistered.
Returned them to the school the next morning, could see teacher give her TA an eye roll, I explained to teacher I've put dd in her trainers as she had someone else's shoes on when she came home, and they'd ere too small an unsuitable, teacher told me she had already checked the class feet the day before as dd got upset about her feet hurting, and these were defiantly my dds shoes, I told her how dd said it had happened at lunch time, when the whole lower years had watched cbeebies in the hall as it was to cold outside and everyone had to remove shoes so as not to muddy the newly laid carpet, I said that dds shoes were clearly labelled with her name and year and were four sizes bigger than this pair, and that I think a much smaller/younger child must have picked my dds up by mistake, she said that the children did not have indoor play the day before and certainly wouldn't be watching cbeebies, so dds story is fully false and handed the small pair back to me. I refused to take them and left them on her desk and left the building, dd who was very upset at being called a liar and I could see her holding back tears at her seat.
Left school calm on the outside but pretty angry on the inside, I'm sorry to say but I rang the school once I'd calmed down and explained what had happened, offered to bring the receipt and packaging for dds shoes up at collection. They promised look into it. I got a phone call three minutes later saying dd shoes had been found on the feet of a reception child, their teacher had noticed the child walking floppy and checked their shoes noticing my dds name inside them. They had in fact spent the lunchtime play watching cbeebies in the hall, dds teacher wasn't aware as she had sent them all outside before going on her break, the weather turned bad and the lunch assistants brought the children in.
To be fair to the teacher she came over to me at the end of the day, extremely apologetic to me and said she'd also apologised to dd for saying she lied and had done some nice activities with her that day as she was upset for being told she was lying, and that she would fully understand if I wanted to take things further. The apology was more than enough. I work in childcare myself and understand how parents can be sometimes, and she is a fantastic teacher in a fantastic school. I'd have been "that mother" in their eyes for a little while though, and can see how unreasonable I was suggesting they check the whole lower schools feet for my dds shoes.