Worst people ever do not buy from them

I fiund these people on facebook. They sell Smart Watches. Now I got connected and we took the conversations to whatsapp. Now not ones did they say anything about a policy they have when you buy a product. So we git a watch from them and when that arrived the back cover was not on it. The watches was not in any good condition. One can see durt ons the back of the watch were the back cover should be and the plastic film on the front did jot look so good to. So I have taken a photo and send it to her and she was like " oh no was there no back cover?" Ok I will phone back. Wated till 7 that night no call. So I phoned a few times and no answer. When I got hold of her she was rude. No when I ask to get my money back she comes up with "oh one of our policies is that we can only do a swop and not n refund and it must be the same price. Now what do I do?