It is likely that the failed bulb triggered a fault code in the diagnostic system, and although the bulb is now working the fault code is still present and will need to be cleared. On this generation of Polo you can try to clear the code yourself by turning the ignition off, holding down the left button between the instruments (next to the zero trip/reset button) turn the ignition to position two, let go of the left button and then press the right button. A second method is to follow the same process but releasing the left button, press it once and then press the right button.

If these methods are not successful in clearing the codes you may need to visit a garage that offers diagnostic services, or you could consider purchasing a suitable diagnostic reader that provides the facility to clear codes yourself.