Shit, I've done this with TrustDice deposit. Arbitrum USDC sent to ETH USDC address.
Naturally, support rep says 'Dear customer, we're unable to help, it's your mistake'
If anyone has a clue what else I can try to persuade them 'to try', I'd really appreciate any tips. I'm a newb lol
There's nothing much you can do if the support won't help you. Perhaps you can keep pestering them if the amount is so huge. For most platforms I have used before, the Arbitrum and Ethereum addresses should be the same so even if you sent USDC Arbitrum by mistake to a USDC ETH address, the account should still be credited unless Trustdice does not support USDC Arbitrum.
There you have to persuade them to start supporting arbitrum network as well if you are to get anywhere close to recovering your funds