How can I fix my cooker - stoves newhome DF600 SI?

Gas Hob with electric fan oven. The oven is permanently on when cooker switched on at the wall power switch but the fan does not automatically rotate unless turn the oven switch on at the cooker. Also it appears the thermostat may not be working as the oven light does not go off to tell me if at temperature just gets hotter and hotter?
What part ot parts need replacing? Can this be fixed without having to buy a whole new cooker?