What would cause the interior light/thermostat housing to over-heat?

Make = Beko (Fridge/Freezer); Model = CDA 752F; Age = 28 months.
I replaced the interior light and thermostat housing, but not the thermostat due to over-heating, which caused the lamp housing to melt into the plastic cover. Both the lamp housing and plastic cover were replaced, but the over-heating still continues, and this time, neither the fridge nor freezer is working. Could the thermostat cause this severe symptom?

Thank you!