Former flame to demand call (7)
I believe the answer is:
exclaim
'call' is the definition.
(I've seen this before)
'former flame to demand' is the wordplay.
I cannot really understand how this works, but
'former' could be 'ex' (prefix meaning former or onetime) and 'ex' is found within the answer.
'demand' could be 'claim' (claim is a kind of demand) and 'claim' is located in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for exclaim that I've seen before include "Cry out (in shock, etc)" , "Blurt out" , "Speak sharply" , "Express surprise" , "Speak suddenly" .)