Can't receive two-step verification texts--Iphone X but not a new one

[Gullyfoyle]

I have had an Iphone X (current IOS: 13.3.1) for a couple of years. I have had the same phone number with Verizon for well over a decade. I have a number of sites (brokerages, banks, ISP, ADT) that use the two-step verification where a text with a (usually) six digit code is sent to my phone. after sign-in. However, recently and for no observable reason, my phone has stopped receiving all such texts. I have to tap the alternative (send e-mail) to receive the code, which works fine. One site sent a voice message with the code as an alternative, so it's not that their number was somehow blocked by my phone. Also, I receive all normal texts. It's just the two-step ones I'm not receiving. And as far as I know it's all the sites that use two-step verification.

I've checked my settings and don't see anything out of the ordinary. I have had the "IMessage-send and receive" button checked, with my Verizon number, since I bought the phone.

I went onto an Apple support site, which said it's a Verizon problem. I went to my  local Verizon  store, which  said, no, it's an Apple problem. I went back on the Apple site which said, no, really, it's a Verizon problem, that I'm not receiving SMS messages. (I don't know much about this stuff, so I don't really know what means except it's different from MMS.)

I've searched this site, and see a number of past postings on failure to receive two-step verification texts, but they seem usually to involve new phones and/or new phone numbers.

Any help appreciated.

[vzw_customer_support]

We are here to help, we don't want you missing out on important texts. Do you have Call Filter enabled by chance?BrittanyC_VZW

[Gullyfoyle]

No.

[Gullyfoyle]

Brittany,

Is that it? No further effort by vzw customer support to address my issue?

[vzw_customer_support]

Gullyfoyle You are currently in the community forum which is usually monitored by your peers. I would be happy to help you. What error message are you receiving? At what point do you run into this problem? Have you ever been able to use it? DoloresK_VZW

[Dawgmother]

Did you ever get a reply?