Iphone X call problems

My phone has been acting funky for several months. People have called me multiple times and not gotten through and I have trouble connecting with others too. To make matters worse, I recently tried a free trial of RoboKiller to stop robo calls. It exacerbated the problem with connecting so I deleted it. After that, I started getting the following text message up to a hundred times a day: RoboKiller received a call from 13524087982 but the app was unreachable. If you want to stop using RoboKiller, you must disable call forwarding by calling ##004#. (Often, but not always with the same phone number). I have tried the disconnect number plus three other disconnect codes over a dozen times which all say they have been effective but I still get a ton of calls like this and frustrating connection problems. The techs at RoboKiller have been working on it for over a week and made no progress.

They are as dumbfounded as I. Is there a way to reboot the phone app? Is there another way to proceed? HELP!