Legal options? If going through normal complaints channels don't work, seek guidance from the regulator. Alternatively, you can file a police report and/or try to sue them.
Did you send the EUR via SWIFT or SEPA? If you sent it via SWIFT, are you sure the recipient account is connected to SWIFT?
Many EMIs don't have traditional SWIFT support and provide another BIC and/or another IBAN for SWIFT (if any at all). Wouldn't be the first time I see someone sending a SWIFT transfer to a SEPA only account. If that's the case, it'll take a few days (or few weeks) for the funds to return, the speed of which depends almost entirely on your bank.
You can ask your bank to do a SWIFT trace, which is different from just a transaction receipt. If the trace shows that the funds arrived, you can ask the vendor to show it to PayDo.