Sorry to hear about your account that sucks. I'm just perusing and haven't caught up on everything. I'm guessing you've been going back and forth with cryptios or someone.

You can always create an electrum wallet - sign a message with that wallet. Then send a small predetermined payment from the wallet you can't sign a message from to your new wallet then send it back.

This at the very least shows you are in control of that particular wallet - much the same as signing a message - just costs some TX fees.

Good luck