Not getting app codes

I have contacted my carrier, AT&T, several times, about the issue, and they have me reset my network settings and other such nonsense that doesn’t work, and, every time, they tell me that it’s on my end. They tell me to make sure I don’t have the numbers blocked, or they ask me to make sure I don’t have the setting set in phone or iMessage to silence unknown callers, etc. I do believe it is a carrier issue. I have done some more research, and there are a multitude of other AT&T customers having the same issue. I just wanted to make sure, before I call them, again, that I wasn’t missing some setting or phone issue. Thank you