My Night Guard Have A Mold, And I Have Used

My night guard have a mold, and I have used it for 1 month only and I take a good care of it , I wash with polident , I brush it with soap and I use it to sleep only.
I went to my dentist today and they don't want to refund me , I am very upset because I pay $475 on it. I would like to have some advise what I should do about it.