Terrible experience I endured after making a purchase.

I recently bought an electric toothbrush that I tried charging with the intention to use and the unit didn't switch on. I immediately reverted back to request that they replace the unit with a proper working one and now I'm told they cannot exchange it because the supplier says it works perfectly. I later decided to request a refund after giving them an opportunity to do the right thing and im now told that i cannot get my money back due to the fact that their return window has closed.