my home country Denmark has a dual tax agreement with Thailand and I got a Thai TIN number which was actually requested by the insurrance company in Denmark that pay out my private pension. So the reason they gave you are contrary to my experience. But this is typical here : different answers different rules for the same situation
can't use that when it has to show international transfer which is necessary if we talk about extension of stay - at least if we talk about non-o based on marriage or retirement and monthly transfers