Hi and welcome to YT.
Im sorry to hear that
What is the name of the breeder or kennel which you purchased your puppy from?
And what wording did they use in the advertisement?
I dont know if you can sue them for false advertisement unless they said they were not a puppy mill.. but im not sure on that one.
I bet there is some sort of legal action you can take though!
Im sure another member will be along with better advice soon, sorry I couldnt be of furthur help.
Hope your little one is doing well and good luck!