How do I clean acrylic + oil wash?

It sounds like you might not have left it long enough to cure. An oil wash should not effect Acrylic paint unless its not been left long enough or you wipweing to hard when removing excess.

Use the white spirits to remove the oil wash.

Just use the same spirits that revoved it before. Wash it in soapy water and start again. Use more acrylic clear to seal, let it dry hard and then use a different thinner.

If you want to completely remove the paint and everything else so you can start over, what I use is a soak in Isopropyl Alcohol 91% or stronger, along with a cheap electric toothbrush.  That will strip it down to the bare plastic (without hurting the plastic or making it brittle) and it will also leave the surface completely clean and prepared for your second try.  Had to do that recently with some F-16 wheel hubs that had the same thing happen to them during a wash with a product I had never used before.  They are all re-painted, re-washed and weathered and look perfect now.