Text messages keep messing up my iPhone?

Ever since I've bought my iPhone 5c back a year and a half ago, it's been completely messed up. The first problem I noticed with it was my back camera started malfunctioning and the flashlight part only worked half the time. Other problems that started happening with it is that it will no longer delete my text messages, which when I try to, it messes up my calling, FaceTime, and it won't let me text or receive texts. I then have to turn my phone off and sometimes that works, but sometimes it keeps those deleted messages on my phone and it takes my phone like 20 minutes to allow me to text or receive texts messages that may have been sent to me in the middle of malfunctioning. Recently, my phone is getting to the point where when I try to text someone, it removes the previous text messages that I had from that person and shows the last thing they sent me. Eventually after 30 minutes, the previous texts come back and I can text them back but if I tap on another separate text message from another individual, it does the same thing and messes up the other text messages. Also recently, when someone has an iPhone and they have their read receipts on, that messes up my text messages and does the same thing, such as preventing me from texting anyone or receiving messages, calls, etc. Starts working fine after 30 minutes. I can receive them perfectly fine if the read receipts are turned off. I HAVE reset everything and put everything back on my phone and I've done everything that you should do when your phone malfunctions, besides taking it to an AT&T store. That's my last option at this point. Is there anything I can do to help fix my phone?