Geld terug geannuleerde vlucht?

I booked flights for myself and three other passengers in Summer 2020 for a total amount of 3507.70 EUR with Thai air. The booking was done at the Dutch website (opodo.nl) of the Spanish online travel agency O. Flights were canceled by Thai air. O. got the money refunded by Thai air. O. asked me to provide bank details for the refund. I gave them the details of my new bank account. But although I gave another IBAN for the refund O. without asking for further information refunded the money on 16-Oct-2022 to my old bank account. This bank account does not exist anymore, because I permanently closed it long before Oct 2022 and opened up a new bank account. Therefore I still did not get the money for the refund. O. states that now > 3 months after the transfer the money is still with the bank (Bunq). I also provided bank statements from this bank account to O. confirming that the money never arrived. In December 2022 O. promised me that they will initiate the transfer again to my new bank account and that it will take max 30 days for it to arrive. Now I contacted their customer service again multiple times and they inform me that the refund was never repeated and the bank (Bunq) still had the money.
I asked O. why they did use my old bank account for the refund although I had indicated to use another one. They just replied it is their standard procedure to use the account which was used for making the booking of the tickets. I do not have legal expenses insurance and I am trying to solve this case without paying a lot of money for legal help. Is there any way I can put pressure on O. to repeat the refund without making legal expenses which I would possibly not be refunded for? Thank you very much for your support!