You cannot perform this action on a system service

UPDATE:

There was an application installed call "Voice Message" that was automatically blocking access to Accessibility and other apps. When I went in to look at my "default apps" "Voice Message" appeared as default for SMS app. I tried multiple times to change it, but it kept automatically changing back to "Voice Message" and then I received the message again that "you cannot perform this action on a system service".

SOLUTION:

• Turned off Wifi, Wifi Calling, Bluetooth and put phone into Airplane Mode.
• Went back into "default apps" and re-set the SMS app
• Went into Accessibility - Installed Apps and turned Trend Micro Mobile Security to on
• Went into Trend Micro - App was now linked to Accessibility
• Went to perform scan, but have to be connected to the internet
• Took phone off "Airplane Mode" and returned to Trend Micro and performed scan
• Scan revealed "Voice Message" as a threat
• Deleted "Voice Message"
• Turned Wifi, Bluetooth etc. back on

My phone is now back to normal