Don’t replace faulty product

My sister had ordered my son a m6 watch for Christmas. When he opened it on Christmas Day, it didn’t charge. We sent an email explain the issue and we’re told to courier it back to them at our cost and once they receive it, they will send a replace it. They received it on the 17 January and I still don’t have a replacement. Every time I email, I get told they are sending it. It’s not easy explaining to a 7 year old that his Christmas present still hasn’t been replaced. This is disgusting service and I will not be using them again!!!!