bismillahir rahmanir rahim
answer; in our country those who clime that their bank is operated according to sharia, in fact they dont maintain the sharia`s law properly. so its not permissible to take extra credit until it knows clearly that whether are they maintaining sharia properly or not:: so for those person who care halal and haram, its better to not taking that; instead this extra credit should be given poor as charity.(ALLAH knows the best)
to answer ; Ariful islam
fiqh dep. iom..