Here are my email excerpts from support back in Sept-Oct:
It is possible in a roundabout kind of way. A voice only line would need to be delivered and then we can port the number over to that voice only line. Then we can cancel the Fusion line. We cannot simply make the Fusion line a voice only line. Voice only has a $150.00 install and the monthly cost including taxes is roughly $20.00 a month.
Unfortunately since we don't have a way to downgrade your current service, the voice-only service must be delivered as a new product. That service would come with a mandatory $150 installation fee.
So the process would be similar to the process you went through to get your current internet installed (Fusion DSL X1). Yes we would need to send a tech out to install the service once AT&T delivers the new phone line. This process would take a few weeks to complete however your service would not be down for the whole process.
Once you verified that your voice only service is working, and you have a dial tone; you'll want to give support a call to cancel your internet portion of your service.
But from my experience, I had to physically move the line from the old to new at the MPOE (this is at an apartment). I didn't see the AT&T tech come by at all, so, I had no clue which one was my new line. I called support and they told me which number it was at the MPOE, but it didn't correspond at all. I probably had to disconnect a few lines to determine which one was my new one.
I've probably dealt with at least 5 members of support during these email interactions, so, not sure why you're getting the runaround.