Last winter the heater in my polo was great very nice and warm. This winter it dont seem to want to get warm so it constantly blows out cold air. Could someone help me on this matter

A few things you can check:-

1) Is the coolant level OK?

2) Is the temperature gauge reading normal?

3) Has anything in the coolant system been changed eg has it been drained to change a hose? This could produce an airlock which will stop water circulating.

If all looks OK then it probably the valve which controls flow of hot water into the heater, either stuck or cable is operating properly.

If the temperature gauge reads much below 90° C when the engine is hot, you may need a new thermostat.