I suppose you've already tried scrubbing but without success. My next line of attack would be meths but I wouldn't be too hopeful. The chances are that the dye has eaten its way into the surface of the vinyl. This calls for more drastic action in the form of acetone.
Go carefully because acetone dissolves vinyl. I've used it in the past to clean up filthy cables and to get the grime out of dimple finish PVC coated panels. A quick wipe is often enough. If the surface becomes sticky you're overdoing it.
If you haven't got any acetone handy you could try nail varnish remover instead. I'm not sure what's in it and brands may vary but I read many years ago that acetone - or something chemically related - was the principal ingredient.
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