Poor quality and service Blackheath branch

I buy from School & Leisure because they have quality that is never disappointing, but on Monday I bought face masks for my boys only to get home and open one to find a thin black mask. I can't use this for my children. They were in sealed packets so I wanted to return the other two that were not opened. I was told I cannot return them. I believe you should have better quality then instead of selling items of poor quality at the safety of our children. Very disappointing ?