I went to pay our TOT bill using BKK Bank billpay which we have been using for that purpose for a number of years.  It wouldn't let me pay saying the TOT account referenced had been closed.  After multiple calls to BKK Bank (useless) and then to TOT (useless at first,) a TOT rep explained that we can now only pay our TOT bill online using the smartphone app, of which change they had never notified us.  So, I entered it into the TOT app and it went right through.  The rep confirmed that she could see that the payment was posted.  

 

I guess it's part of the general replacement of computer and website access with smartphone app access.  Not my preference, but there it is.

If you don't like paying with a smart phone you could consider paying via automatic payment. Once set up everything goes automatically and without problems.

I think it's a while ago that this method didn't work anymore.

Maybe related with the CAT/TOT merger?