True pay as you go sim

Is this concept dead ? I can’t find a single sim that allows you to top up once and then have many months or more of credit validity (as long as you don chargeable event once every 6 months or so). All I can find is monthly rolling deals around £5/m. AI answers do keep referring to giffgaff for example doing as I described above (credit doesn’t expire if you use some once every 6 months) but when you actually go to their website it doesn’t exist.