I don't know how they got in, and I don't care - I just want them GONE.
Google is your friend, so off I trot to find the solution. Only I don't find the solution, I find a whole range of options, none of which is anything LIKE the "nuke-em-from-orbit" answer that I seek.
I can spend a HUGE amount of money on an ecologically friendly, bio-degradable spray that acts as a deterrent, and lasts a few months.
I can spend even MORE money on a less degradable deterrent spray that lasts a few years.
What I CAN'T do is spend my money on something that will KILL THE DAMN TERMITES - NEST AND ALL. Why? Because the pest control companies are not allowed to sell it or use it, even when the manufacturer is still allowed to make it, in the name of the environment.
Years ago, my father and I renovated an old mud-brick farm-house.
The floor was gone - joists and boards eaten by termites and turned into fancy insect architecture made of dried termite spit.
We removed all the damaged wood, and then deployed that great insect leveller - DDT - liberally. New joists and boards installed, a coat of plaster, several coats of paint, new stove, new window frames and glass - house habitable again.
The best bit? No more termites - EVER.
The ability to do that has not been LOST - we gave it up, for nothing, and that makes me sad.