USSD Code Problem

I am having g5 f700l model (korean version). I can use three digit USSD code. But 4 digit USSD code is not working. When I am trying to use 4 digit USSD code, it appears calling screen instead of USSD menu. Is there any solution? May be in Korea there is no 4 digit USSD code. I am using it in Bangladesh and most of the USSD code is 4 digit. :(