weird activity on iphone 5s?

Hello,

I've been noticing some strange activity with my iPhone 5s lately. I was typing a message and when i pressed the "c" key it deleted the entire text! The message was blank and this has never occurred before.

I also noticed there was a blocked number on my phone that I don't remember blocking, I looked back at my bill and saw that this number has been texting me for almost a year now! I never replied, assuming because the number was blocked and the messages didn't show (it still shows on the bill).

I unblocked them to see who they are, gave them a call, and got error message pps6180 (meaning it's a payphone with no minutes).

I don't remember blocking this number at all. Could it be that someone has access to my phone? I've only had the 5s for a few months. I hope I am being overly paranoid.

Thank you :-)