@Paul ******
you shouldn't need the Thai insurance to do those things because your visa was issued before the new requirement came into force.
That is how it should be and how it has worked for many people.
However, not all immigration officers enforce the same rules and it hasn't been that way for everyone.
Carry a copy of your travel insurance certificate and if asked tell them you have insurance but because your visa was issued before October 31st 2019 you don't need it.
Hopefully there will be no further problem but if they and their superior officer still require Thai insurance they *should* stamp you in for 30 days so you can buy insurance (at least this is what they have been doing).
If you arrive on the 28th of January and leave on the 26th of February 2020 you will have the option of doing nothing or going to your local immigration office as detailed below.
If you arrive on the 27th of January you will need an extra day.
You should go to your local immigration office and tell them that you were stamped in incorrectly.
They should correct your stamp to a 1-year stamp.
It may also be possible to extend the 30-day stamp for another 30 days, just like a normal 30-day stamp. However, I have no idea if it actually is possible and I don't remember seeing reports of anyone trying it.
Nothing is certain. While a number of people have had their stamps corrected that way, one person recently posted about being refused the correction Chiang Mai immigration.
How pre-October 31st 2019 O-A visas are handled seems to be down to the luck of the draw but with the odds in your favour... at the moment. Tomorrow might be different.
Keep an eye on this group or ask again before you return.