We have a small business with several signs on our building and another big sign on a building opposite a shopping centre. 

 

The latter one has English narrative - 10 letters to be precise. Its costing us an extra 15000 baht bc we have English on the sign. 29k bill for that sign based on the size 

 

I was wondering if theres any way to double check if they got it right or not. I asked one of the lovely ladies to check it with the manager but think they didnt bother. 

 

Any opinions are appreciated. 

This is normal.

Take a look at this website, there is a lot of info explaining it all and a section with a right of appeal if one thinks the tax has been assessed unfairly.

 

https://www.octopus.co.th/en/blogs/how-to/signage-tax-thailand