I just wanted to pass some information on to you.
I received a bill in the mail from Texas Tollways. (I found out this is different from NTTA)
I thought this was strange as I have two current tolltags with balances on them. I called them up and it turns out I got charged at the new toll portion of 121 in Lewisville.
I assumed it would be deducted from my NTTA account. I assumed wrong.
When I called NTTA they said since I had a "Cash Account" whatever that means, I was not in the system to approve the charge. The rep took care of it for me so I will not have issues in the future.
You may want to call NTTA to make sure you are able to use the new toll portion of 121 with your toll tag.
NTTA Website has contact info on lower left side.