Hotpoint RLA84 Dead

Last Friday I noticed the fridge was dead an light not on. Wifey was demanding, whilst holding a rolling pin, that I fix it so, checked socket and plug etc and all ok.
Changed stat and it worked. Although light still off so checked bulb and its dead. Now the firdge works but ice is forming on inside back of fridge no matter what setting you have stat on.

4 years old

Only 3 connectors on stat and one of them is earth so cant’ do wrong, or can I?
Used a universal stat as per shop ex engineer say so

Any help appriiciated and could save my life or a severe battering from my old gal. 🙁