THis is a very simple case. You should have returned it to the store the same day for a full refund. The law says that as long as you have a receipt you can exchange any product within 14 days of purchase and some products within 30 days of purchase. If you have receipt you can go to consumer protection agency and file a complain. Also you can call them.. their number is posed in every shop.

The trick here is that I think the retailer waited on purpose for 14 days before telling you off, so he thinks he is off the hook. but I dont think so. especially if you had someone with you during your visits to retailer... you should definitely stand for your rights. because if you dont..nobody will