The operating carrier is responsible - in this case Jet. Do not deal with anyone else (travel agent, etihad). Decide on what would be proper compensation if anything (travel voucher, money, miles) and ask for it in writing. It would be good to understand and outline the alternatives they could have offered (e.g. rebooking on another airline, hotel outside of the terminal) as a 24 hour delay to London seems unnecessary when connecting at AUH (there are 3 EY flights a day).