Hi. Thought I would share my wife's visa extension story in case it helps others. She is dual Thai / Australian.
She entered Thailand in late March 2020 on her Aussie passport and received the 30 day stay upon entry. She did not use her Thai passport as it had long expired. She renewed it in April 2020 in Bangkok.
Immigration at Chang Wattana advised if she went to her home province, explained the situation, showed house papers, filled in the TM7, etc she would get a one year extension in her Aussie passport
Couple of days ago this was successful at Bueng Kan immigration.
In hindsight we should have renewed her Thai passport but felt that it was not much value to do so since it is not an easy passport to travel on. I have also since learnt that you can enter your country of citizenship with an expired passport or ID card, but this can cause delays at departure check in / port of entry as it is a bit unusual.
TLDR : Answer Summary
A dual Thai/Australian citizen shares their experience of successfully obtaining a one-year visa extension in Thailand using their Australian passport, despite their Thai passport being expired. The process involved visiting the local immigration office in their home province, where they provided necessary documentation and completed the required forms.
