Had not been receiving SMS text messages to my iPhone number (resolved)

(Other Xfinity mobile users have reported similar problems on this forum, but their report tickets have been since closed, so it seems no further follow up replies are possible on those threads)

Since porting my service from Verizon to Xfinity Mobile, I had not received any SMS text messages to my service mobile phone number.  Account authentication codes from Amazon, IRS, etc. were not coming through. 

Customer service found that my account had "Premium Text Blocking" (an anti-SPAM feature) enabled. When customer service turned this feature off, text messages starting coming through.  No changes were needed on my iPhone.  Only changes were on the Xfinity side.