The wrong size of the very same sneaker 3 times

I ordered a pair of UK 7 Vans online. When my son wanted to wear it, he realized it is too small. It was over a weekend so I sold it to my sister. It was a UK 6. She then opened a Superbalist account and ordered a UK 7 again, to replace the ones I sold to her.

She ordered a UK 7 and again received a UK 6.

She logged an exchange for a UK 7 and again received a UK 6.

This is a waste of time. Do they not check the sizes before it leaves the warehouse. Do they not double check the size especially when it's a return or exchange. This is really disappointing.