We have double checked your case carefully, here are replies:
I am unable to see the BTC address I originally entered when setting up the account.
Because you pressed 'Lock' before inputing your BTC address, so BTC address is empty, and you can not add/change any address any more in your side. This problem can be fixed via sending your registered email address to us (PM is also available).
I am unable to change or add an address for BTC. withdrawal.
Ditto.
Please also PM us your BTC address to get earnings earned before you are able to set a BTC address by yourself.