Is this a Valid XFinity Retention Number? 1-855-726-9715

I went in to my local Xfinity store recently after noticing a significant increase in my monthly bill after my promotion period ended and I was given the above number 1-855-726-9715, told it was the direct Retention line, and said to give it a call to see if they could work with me on reducing my bill.

I called the line and the individual on the other end said there was an upcharge and then connected me to what he called the "Cancellation Team" who said they needed to login to my desktop virtually (they had me download UltraViewer virtual desktop) in order to send me a link to "Refund Form" for me to fill out (they said they couldn't just this to me via email, they had to login to my comp remotely and manually pull up the webpage form itself on my browser). I needed to fill out my name, address, phone/email, and my bank name ( but not checking account or routing information) on the said form and submit.

Apparently there was an issue processing my refund and they said they would try again tomorrow, but I am concerned about the whole logging in remotely through my PC and I just wanted to make sure this was a genuine customer service/support line I called? I was given this number directly by an instore Xfinity associate but was taken aback by why they needed to login into my machine directly.