Never again (4)
'never again' is the definition.
(once can mean one time only)
This is all the clue.
(Other definitions for once that I've seen before include "'... bitten, twice shy'" , "Cone (anag.)" , "In days past" , "At a previous time" , "in days of yore?" .)
(Other definitions for no more that I've seen before include "opposite of what Oliver wanted" , "Monroe (anag)" , "Nothing further" , "That's all - finished" , "Never again, that's the end of it" .)