Water pressure flosser

I bought the pressure flosser and when it arrived it did not work. I took it to a Homemark store who said that they could not exchange it as it was bought online. I have send emails to the various people online and they just choose to ignore me Portable pressure Water flosser order number is 49171A Please can someone explain to me how I exchange this faulty item or get my money back. Actually by the way I am being treated maybe its best I get my money back and never shop there again