iphone 6 wont stay connected to my local WIFI.

All has been reset as to Apples suggestions incld my modem ( Unplugged, reset, nothing interfering) and whats avail online, Resetting my phones settings, forgetting the network, etc etc. it will connect for a couple minutes then I wont see that it says LTE after a long period of it using my data. Just got the text today that I'm already way over my data usage. This issue has just happened in the past week. Haven't done anything as to updates etc. IOS 9