Yeah i know that feeling. I wasted 23 motes of light last week week on a chest piece engram and got a stupid titan class ( i'm also a warlock ). So Xur realised his mistake, apoligised and gave me some good **** this timei bought 2 f***ing exotic engrams.
one was for hunter (i'm warlock) and the other one was the helmet you can buy for warlocks from xur.
i save my coins and hope that xur has the nemesis-helmet in the next weeks.