cannon henley 600 model 10430g oven remains on in the 'off' position?

for the above model, I have replaced the main oven thermostat as it was faulty after many years use (oven did not heat up, interior light and fan working. Changed element first, did not resolve).

Changed main oven thermostat, oven now heats up to desired temp set by switch. However trying to turn oven off at switch (set to 0), oven fan & interior light remains on. Temp reduces to zero (as expected) but to turn off oven interior light and fan I need to switch whole cooker off at mains.

Any suggestions? Anyone had similar? I know there's one post here from 2011 where similar problem experienced, but no replies to it sadly.