Poor customer service.

Yesterday the 23rd of December 2023,I bought a sneaker @Tekkie Town in King William's Town,MetLife Mall.The Vans sneaker was a bit dirty but I took it anyways as it was the last pair...upon realising that the shoe is small,I return it back.Now they claim that they won't take the shoe back because it's dirty.Now I'm asking them what do I do as it is suppose to be worn on the 25th.Before coming to the store I phoned and the manager said I should bring the shoes but when I get here they telling a different tune and the manager I spoke to is from another store not tha actual store that I bought from.They claim it's a shop Soil and it wasn't suppose to be on the shelf,but it was actually there.Its a matter of who is telling the truth between me and the store..whether they didn't notice or their case they claim that I made the shoe dirty.Can anyone please shed a light on how I should resolve this matter as I need a fitting shoe for my child for Christmas.I don't have another R750 for a shoe and have no reason to keep a new,small shoe.I would appreciate if I would get a response as I'm still in the Store waiting for this issue to be resolved.