[V6-12v] Oil Change question

[Nathan Widmyer]

I went to change my oil last time and used a crescent wrench.  I rounded off the oil drain plug and had to get a pipe wrench and some more muscle to get it off.  I bought a new plug and put the new nut on.  I went to change my oil again recently and I used the wrench provided in the wheel well in the trunk made for the nut.  I couldn't get the wrench to grip on the nut to move it.  I sprayed WD-40 on it several times, no luck.  I got a pair of vice grips and tried and the teeth only made teeth marks in the plug itself.  Before I damage the nut any more, what is the right thing to do because I can't seem to open the plug without destroying it.  Thanks in advance, Nate.