there is widespread non compliance and zero proactive enforcement. The RD auditors are fully employed just dealing with criminal referrals. The Finance Minister in a recent interview admitted that the RD had not carried out a single proactive audit on any business in the last five years. The idea that somehow they have the resources to start auditing PIT filings is ludicrous.
The fee is for applying. You applied and was charged the appropriate fee. No refund. You can apply again and will again be charged the appropriate fee. Life lesson, understand the MRZ on your passport.
Expats who reside in Thailand over 180 days in a calendar year automatically become Thai tax residents. As a Thai tax resident you are required to file a tax return only if you have assessable income. Thailand does not tax on worldwide income but only on domestic and foreign sourced remitted income.