My S21 phone stopped getting firmware and security updates

I checked my S21 phone and noticed that the last update occurred at 3:02PM on March 24, 2026.  My latest update information is as follows:

One UI version: 7.0

Android version: 15

Security patch level: January 1, 2026

I am concerned that my phone is vulnerable with this level of updates.  I talked with Samsung's live chat and they said Xfinity had it locked for updates and I should contact Xfinity.  Could this be true?

Thanks for any information.

Jim