Return Policies only apply for certain buyers

I ordered a King Large duvet inner and a King Large duvet cover with pillow cases. The duvet inner was a Queen size inside a King Large bag, a used item - nothing new about this, they regularly do this. I sent that back while waiting for the duvet cover set. I was informed that the supplier for the duvet inner was out of stock and credited me. I purchased one at Mr Price and waited for the cover set to arrive. It came eventually and I opened it up. Looked perfect, washed it before putting it on my bed. Then I noticed the duvet cover is not the right size, there's also no size on the tags. I logged my return just to find out it was denied because i washed it. Up until today they cannot answer me what the size is. They refuse to exchange it due to them sending the incorrect size. They're return policies state that they do not return washed items but why do I receive so many used items and items that was returned. I even had items where the previous buyer left his return note inside and packaging was damaged. They clearly allow this. Double standards and pure incompetence and lack of work skills.