The cause could be (in order of cost to repair):
Kinked radiator hose, unlikely given the previous attention to the problem.
Defective temperature sensor or dash board gauge. Can be checked against
thermometer taped to upper hose.
If, despite the fans running constantly, the engine runs hot both in
slow driving and at speed (90 km/hr) the radiator is plugged up (inside
and out) and ought to be professionally cleaned by a radiator shop or
replaced (especially if it has plastic tanks).
Blown cylinderhead gasket, unlikely unless there are other symptoms like
rough running, oil use, oil in coolant / coolant in oil.