I have had this same probelm of a horizontal line with upward pointing arrow which just appeared suddenly yesterday. I have followed your instructions, deleted all missed calls and cancelled all call diverts, but it is still there!
It might be "call divert", which means all your incoming calls are redirected automatically to other number, usually to your voicemail. To check the status of diverting choose Settings from menu, > Call settings> Call divert> ... >Check status or if you want not to divert anymore > Cancel.
An arrow icon has appeared at the top of my screen. It is a horisontal line with the arrow head pointing vertically upwards. What is it and how do I remove it?