Not trying to step on inzone's toes, but.. Norton is garbage to be honest, in every single way, shape, form, and platform. In fact the Symantec corporation has a history of making rogue programs and apps that purposefully glitch out and make wonky things happen to try and scare you into buying their software when the trial version runs out.
If you go with any mobile antivirus solution - get ESET.
The installation requires a complete wipe of your phone which includes messages and pictures etc etc (so make sure you back everything up), and will install a rather robust firewall which should prevent any unauthorized access.
The wipe IS necessary as it will remove any kind of spyware or tracking information that has been implanted on your phone and restore it to the way you bought it - plus added security.
Or as inzone also suggested, just get a new SIM card.
Personally I don't use any kind of antivirus at all, even on my PC as I find it needlessly bogs it down and eats unnecessary resources. It's all about awareness and knowing what to trust in the e-universe. Once a month or so I run Malwarebytes to be sure it's still clean, and then remove it again.