I see this is a really old thread but there is now plenty of information on this.
the melted crayon smell is from German sourced materials that use paraffin wax.
in this case the culprit is apparently the insulation under the carpets and in the trunk.

while products like Pooph are like magic for biological odor sources they won’t do anything for a chemical smell like this.

a thorough cleaning and treatments with an Ozone machine will work but the use of Ozone treatment needs to be limited because it can degrade plastics, rubber. Adhesives etc…

It can be managed with Ozone, deep cleaning, carbon filters and airing the car out.
But based on what I’ve read these things will be most effective only after the insulation is removed and replaced.