I don't know if you can get your used quota back, because as per the EL terms of service, they say that:
#Closed
fleet grove
@agile hedge
But I think if you really think you wasted a ton of paid credits, you might choose to submit a request through https://help.elevenlabs.io/hc/en-us/requests/new but I don't know if they'll consider this or not. It might be worth a shot
¯_(ツ)_/¯
fleet grove
@agile hedge you can open a support ticket in #1156635792962240532 to talk to a member of the staff/mods