Getting fined by NTTA when i have a TxTag. Help needed.

New to the country earlier this year. As I got my vehicle here I signed up to TxTag. My research at the time showed that although there are a few providers, txtag works everywhere in Texas.

Now over the recent time I have been away a lot and have not been able to keep up with mail. Upon checking recently, I have received multiple mails from NTTA to pay them for toll, with increasing fees at each time.

The date registered in the notice is around a time that I definitely had the txtag installed properly as I can see other transactions there at the time.

I called ntta to dispute this, but they said they can't do anything I just have to pay the huge fine.

What should I do here? I have a valid txtag and it's installed properly. Sucks that the system didn't pick it up this one time and is now fining me for it.