Extra cost made gent go on the attack, according to the teller (9)
I believe the answer is:
surcharge
'extra cost' is the definition.
(a surcharge is an additional cost)
'gent go on the attack according to the teller' is the wordplay.
I cannot quite understand how this works, but
'attack' could be 'charge' (charge is a kind of attack) and 'charge' is found within the answer.
The remaining letters 'sur' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'made' acts as a link.
Can you help me to learn more?
(Other definitions for surcharge that I've seen before include "Extra payment" , "addition to bill" , "Additional cost" , "Additional sum demanded" , "More to pay" .)