Thanks for the feedback here before to try Line.
I sent messages in Line with English and google translated Thai included.
When they answered, all in Thai.
So for this year's tax I contacted them on Line to announce I wanted to pay by bank transfer. No response after many days, so I just paid it and included a message and pic of the transaction.
I identified myself with my name and Owner Code which I found on this year's bill.
I think the deadline for this year's bill was actually end of June, not July.
The deadline for previous bills was today.
Anyway, after several days, they did send an acknowledgement that they had received the payment but also some very incoherent info about a previously owed bill or bills from years back. It did mention small penalties for overdue bills. But what they didn't tell me is exactly how much to pay to clear all previous bills INCLUDING PENALTIES.
So I sent multiple messages over several days asking for that information.
Finally, TODAY which is the last day before the deadline they did send that so I paid that by bank transfer. A ridiculously tiny amount of money, but happy to get it cleared.
I'm not sure if you can pay after today if you know what to add for the penalty or not.
Maybe they have a payment window and only accept payments at all during that time. Don't know.
So the moral of the story is that this can all be done with Line without knowing Thai but you need to be very very patient about expecting responses.