can be "de" used here instead of "hanem"?
Not really, no. You could do something like this for "de":
"A banknál nem, de az étteremnél igen." - At the bank, no, but at the restaurant, yes.
But the "hanem" above really stands for "but instead/rather".
It didn't accept "nem a bankban honem a étteremben". Is this wrong?
In English "at the bank" means more "in the bank" than "by the bank".
nem a banknal hanem az etteremben.Why is this wrong,please?