Hi
I think I am right in saying that as long as you have registered your phone in your own name and that you have set up a password to access the Turkcell website while you are not actually in Turkey, then yes, you can use any card (in your name) to top up your phone on line.
I did this not so long ago and have been able to use my card to top up credits on line with Turkcell.
hope this helps
mibur