Not the first service requested by Oliver Twist? (6,7)

'service requested by oliver twist?' is the definition.
'second helping' can be an answer for 'service' (thesaurus). I am not sure about the 'requested by oliver twist?' bit.

'not the first' is the wordplay.
I cannot quite understand how this works, but
'not' could be 'con' (I've seen this in other clues) and 'con' is present in the answer.
'first' could be 'i' (I in Roman numerals eg Elizabeth I) and 'i' is found in the answer.
This may be the basis of clue (or it may be nonsense).

Can you help me to learn more?