1.3 combo van oil filter housing

[uncle peter]

Hi all,i'm new here & i'm hoping somebody can help.last time i did an oil change on my van when tightening down the grey plastic dome that covers the oil filter,the plastic hex head on the top cracked.The time to change the oil/filter has come around again.fearing the plastic hex head might split further i went to the dealership & bought a replacement cap.On trying to undo the thing-using the correct socket & t-bar,half the thing cracked off-just the hex bit,the rest is okay.There is now less than half a hexagon left,so cant use a spanner or socket on it.Any ideas how best to get it off??????(frustrated)thanks in advance of any advice,great site