Renault Service affecting warranty

Given the current legal stance of being able to choose not to have your car serviced at a dealership whilst under warranty, one would imagine that the staff at the dealership would be more efficient. Over the past month I have dealt *********** receptionists to *********** service consultants (Jade)who to date are unable to assist me with the query of which service centres are approved without the warranty being affected. She did not bother to return any of my many calls and today keeps me holding while she screams across to her colleague. I called Renault Customer centre head office and they too cannot assist at this point