I suspect that globally, that heat kills more people than cold, since there are large populations, many of them very poor, in hot climates.

In colder climates such as the UK deaths from cold almost certainly outnumber those from heat.
In many cases elderly people die at home, and even an expert can not reliably determine the direct cause of death. Cold ? malnutrition ? heart failure ? or general frailty and old age ?

Likewise if a younger person dies whilst out running on a hot day, it is often debatable as whether they died of heat or heart failure, or some long standing medical condition.

Cold is easier to prepare for. All but the very poorest in most cold climates have access to warm clothes, warm bedding, weathertight homes, and at least some heating.
(the very poorest DO die in cold weather)

Much less can be done about heat, apart from air conditioning which is beyond the reach of many in the tropics.
Having to perform physical work in hot and humid conditions is inherently risky, and weather just slightly hotter than the norm can lead to substantial loss of life.