You're welcome on no occasion (3,2,3)
I believe the answer is:
not at all
This clue is a double definition.
'you're welcome' is the first definition.
(I've seen this before)
'on no occasion' is the second definition.
(thesaurus)
(Other definitions for not at all that I've seen before include "Never!" , "My pleasure" , "Anything but!" , "denial" , "Don't mention it!" .)