you got "flagged" in the central computer system of Immigration, which means if you try a border run after January 6, it will pop up on the computer of every border officer, and you need to have a "plan B" ready in case you will get refused entry. . . Sorry for the bad news but it is what it is. Don't try to extend stays in Thailand solely based on visa-exempt entries and their extensions. Get a proper visa that fits your purpose, like a multi entry tourist visa or a DTV based on "Soft Power"
the 7-days are NOT an extension. The 7-days is a stamp that says "application denied, you have 7 days to leave the kingdom" and it will cost 1900.- THB
closed on saturdays and sundays, and closed on December 5th (Bhumipol's B-day, and on December 10. If you really want the 7 days on top, then you need to go on the very last day of your existing stay permit. Can't apply one or more days earlier
the problem is, the 7-days grace period starts on the day your application gets denied . . you gotta figure out how that plays with your timeline. It means that if you visit Immigration on the last day of your EOS, the 7 days start the next day
„and for some reason the IO gave me a visa expiration date of 29 November 2025”
No. He didn’t give you a “new visa expiration date”
He gave you a STAY PERMIT which is valid until November 29, 2025
Your “visa expiration date” is still December this year.
After the expiry of your visa validity, you have no re-entry permit any more.
So if you were to exit Thailand in February for a few weeks, you would need to buy a single re-entry permit in order to keep your stay permit until 29 November 2025 alive.
You do not have to do the “1-year extension of stay permit” by next week, yet.
You can wait until 29 October 2025, before you apply for the “1-Year Extended Stay Permit”
my guess, you weren't just warned, you also got "flagged" in the Immigrations central computer. So any Immigration official would be able to see that you have been warned previously. I would heed James Miller's advice
you can only register online by yourself, if your landlord gives you the login-ID and the password. By this you wouldn't waste his time. Maybe he will agree