If changing gear oil, get the new gear oil filter too. If its still same after oil and filter change i suggest show it to good VW mechanic and dont ignore. In Golf and Polo small problem should be attended immediately before becoming serious issue.
In such situations there are a number of things affecting the smoke.
engine oil is burning
rubber valve stem seals have perished
radiator is leaking
get the car checked and you will know what when wrong.
My friend get this Issue repaired ASAP or else you will have a major expense to either repair or change the radiator.
Get the coolant temperature sensor if it working correctly and even the switch and fan relay.