Upvote:2
I am a bit surprised that the Dutch consulate would not cancel the visa but you can definitely apply for a new visa from the Spanish consulate and combine two visas to cover your trip. This particular scenario is even offered as an example in the Handbook for the processing of visa applications and the modification of issued visas
Example: A Moroccan lawyer representing a gender equality NGO who frequently participates in meetings in various Member States holds a multiple-entry-visa which expires on 31.5. She applies for a new visa on 15.4.
If a new visa is issued, it should be valid from 1.6. and in such a case the visa holder would be entitled to enter the territory of the Member States on the basis of the first visa that will expire during the stay and leave on the basis of the new visa.
If VFS is not willing to help, you could try to quote that and the answer from the Dutch embassy to convince them to forward your application to the Spanish consulate.
See also Schengen visa "refresh" and Traveling on back-to-back Schengen visas