You should have turned round and looked at the fire, theres a hole directly behind where the control switch is located when in position for one end of this cable and it's chucky plug to come through from behind the fire
(£1 coin to give scale)
Didn't realise you have Truma's twin heat exchanger 5002 fire, so much deeper to look for cable or the hole right at the back, have a look where I've marked