Ur visa is expired mate. Immigration only do extensions of stay. If you go to immigration I guarantee you will get arrested or have to pay a back hander for them to get you a visa which will be more than paying the fine at a air or land boarder. Trust me.
If its under 90days pay at the boarder you will have no problems. Do not go to immigration centre they will not be able to give you a visa so will be deported no ban but a load of hasle.