Help with accessing website not showing on Port 80?

Hi.  I am a graphic designer and manage/design client's websites (built with Wordpress and hosted on Bluehost).  I have AT&T UVerse internet, and have had it for six months with no problems.  The other night, I tried to access a client's website on the Wordpress backend and suddenly received the following error message:

Forbidden

You don't have permission to access /wp-admin/ on this server.

Additionally, a 403 Forbidden error was encountered while trying to use an ErrorDocument to handle the request.

Apache Server at www.beyondyogatn.com Port 80

I have *never* had this problem before, and I did not change anything on my gateway recently.  I have the Pace 5268 gateway, and have tried numerous fixes, including contacting AT&T, of which they tell me this is out of the scope of their normal techs' expertise and they have to connect me to another department at AT&T, of which I will have to *pay extra* to get this fixed.  This seems unethical and unfair to me for my service to be working normally one day, and then the next not, and I have to pay to have my service restored to "normal".

I have had numerous AT&T techs tell me they have "updated or changed the settings on my connection, and it should be working now", but none have worked.  I have also followed this article with the help of an AT&T tech, and nothing worked here either, despite his repeated reassurances that he would have the issue corrected: https://www.att.com/esupport/article.html#!/u-verse-high-speed-internet/KM1123072

I am at my wits end, as I cannot access my client's website on my home Wifi.  When I connect my laptop to my iPhone's hotspot connection (which has service with Verizon), I *can* access the client's website, so I do know that it has to do with my AT&T service/gateway. Has anyone else had this problem, and if so, how did you remedy it?  I am on a Mac, OS Sierra, 10.12.3.

Thank you!

Heather