Getting support???

You're right the front-line reps are not familiar with traditional phone service. Supposedly if you say landline at the voice prompt you get routed to the landline group, but recently some have said that doesn't work so your best bet if you aren't getting the service you're paying for is to file an FCC complaint. 

@spoom2, thanks I am looking into the FCC complaint already; unfortunately, it appears they used the 10th Amendment to the US Constitution and redirected it to the state authorities before you can complain to the FCC from what I have found so far.

In all the people who've filed an FCC complaint that's the first I've heard that. You just go to their website and file the complaint, which they file with AT&T. 

I am having the same problem.  Try as I might, I cannot get an online account for my landline, cannot set up recurring payments etc.  It always assumes I am talking about my cellular service.  I've tried every way possible but it always comes back to "that service not available".  I want to keep the POTS line, as it will stay up in a power outage, which we get.  I know they want to get us all off the landlines.  Are they going to do away with them?  Just letting the service die on the vine, so to speak?

@KPH You're not having the same issue as the OP as theirs is service related not website related. See this topic

@spoom2 here is the reference from the FCC...

Does the FCC regulate all telephone issues?
No, complaints about your local telephone company or intrastate issues (within your state) should be directed to your state Public Utilities Commission.

https://www.fcc.gov/general/faqs-telephone

FCC consumer complaints