Ok, that makes perfect sense. Anyway, I could recover the BTC with the help of the person.
Now I'm also trying to recover the BCH from those same addresses. What would you advise to do to do that? I tried just relaying a BTC transaction on the BCH network to transfer the coins but BCH transactions must have an additional opcode to avoid chain jumping.
It just uses a different signature mechanism to prevent replay attacks...
I assume the person that helped you, just gave you a "unsigned" transaction that you then signed and broadcast? If so, just use the same unsigned transaction and sign it with the "BCH signer" instead of the default one... refer:
https://bitcointalk.org/index.php?topic=2070058.0Then broadcast that transaction on the BCH network... try
http://blockdozer.com/insight/tx/send or
https://pool.viabtc.com/tools/BCC/broadcast/