"Enable Modes" is grayed out, thus can no longer change my mode from Away to Home

As always, when I left on a trip three weeks ago, I changed my Ring Mode setting from Home to Away.  Upon my returning home, my device no longer allows me to change the Mode back to Home.  Under "Settings," then "Modes and Automations," the "Enable Modes" command is grayed out.  If I tape it, a notice comes up stating that I need a Ring Plan to change the Modes. But I have always had a Ring plan and have not changed it!  I am still on the "Protect Basic" Plan.  Has this plan's functionality been downgraded to no longer allow me to change Modes?  What's happening?  Why has "Enabled Modes" been grayed out?