iPhone has sent random text messages to various contacts, made calls and browsed websites

On three occasions my iPhone has sent random text messages to various contacts, made calls and browsed web sites. The first time this happened I was advised by Apple to change all passwords and build up a completely new handset. This I did but in November it happened again so this time I changed all passwords again, I factory reset the phone and manually built up the phone config. Now exactly one month later it happened again. Have reset the phone, passwords again and limiting apps on the phone. I am running the latest IoS and have Norton 360 with VPN enabled. To stop other people being impacted I now turn airplane mode on when not with the phone which kinda defeats the point of having the phone in the first place. What I found on the second occasion that the phone tried calling/texting etc even in airplane mode so there must be some malware on the device. Any thoughts/help would be greatly appreciated!

[Re-Titled by Moderator]