IPhone Update Issues

Hello, I just recently updated my iPhone, and it deleted every single song that I had recently purchased. I checked for them in iTunes (since it said at the top of the screen that it was "backing up my iPhone") but I couldn't find them anywhere. So...I'm stuck as to what to do, and really ticked off. This isn't the first time a problem with updating my iPhone has happened, but this is the first time iTunes has deleted my songs. Is there any way for me to get those songs back (there are quite a few) or should I write a letter/email/call Apple to complain? Thanks.