iPhone iOS 14 set "Keep Messages" to "30 Days" but not deleting
Finally got my dad from AT&T (no signal at his house even) to Xfinity Mobile (as we use/enjoy ourselves), but on his iPhone SE 2020 (transferred from his previous old non-iPhone phone at the Xfinity/Comcast store), the usual method to delete old text Messages doesn't seem to be working.
iCloud is definitely not On for the Messages app or involved at all, but going into his Settings/Messages and changing "Keep Messages" from "Forever" to "30 Days" warns about deleting older messages, and when he confirms it does then have the "Keep Messages" set to "30 Days," but even after a full Off/On cycling, his old messages are still there.
I know this is likely more of an Apple iPhone peculiarity, but asking here in case other Xfinity Mobile users have experienced this. And being that my dad is 93 and, uh, not that swift with technology, and I am helping him merely via land-line phone and Mac desktop screen-sharing, I'm figuring any hints night help! He previously never bothered with Messages at all and we hope to get him to use texting now, but his old messages kind of upset him, so just ignoring all of it may not be an option. And, uh, many of those old Spam/Junk messages are fairly rude and/or "provocative," as in click-bait or worse...
Rich [Edited: "Personal Information"]