I'm now having trouble with the next step: signing a message with the wallet I used to pay for my Copper membership to prove ownership.
The issue is that it's been a long time since I made that payment, so I don't remember which specific wallet I used. I believe it was an exchange wallet, which I understand is not ideal for this purpose. I'm hopeful we can find a better way for me to verify my ownership soon
Did you used any other wallets when you were using your account (which is old enough and doesn't belong tto an exchange)...? Because you won't be able to sign a message from an exchange wallet. You need to have the private key to your wallet in order to sign a message, and exchanges doesn't give you that key for your address.
Btw, OP did you have secret question feature on? By reading some of the replies it seems like you got your account self banned, if indeed secret questions were used!