Why does my iPhone not say 4G or LTE anymore?

I had a huge phone bill so my parents turned off the data for my phone and now where it used to say 4G or LTE it is blank? Also I can't turn on iMessage unless I'm on Wi-Fi?

Same thing happened to me. I used to have Internet wherever I went but one day ATT shut down my data since I was using to much of it now i can't get internet unless i'm on Wi-Fi. My imessage still worked though. I'm still working on it. Best thing to do is call your carrier.