What store region are you using?There is a scheduled time once a day when updates are released. You have to make sure your phone is connected to the Internet during that time. Problem is, the time keeps changing. UK region now updates app at around midnight US ET. For weeks my phone didn't receive updates because the update sched was changed again. It used to be around 7AM US ET. You just have to find that time.
Microsoft should sort this out really.