Prevent orientation change on USSD request

Question

I have an Activity which i've added android:screenOrientation="landscape" to the Manifest file.in this Activity i Call a USSD request which works fine but it changes the orientation to portrait (when it's sending the request) then it changes to Landscape again when it finishes the process.here is my USSD Code :

String encodedHash = Uri.encode("#");
String ussd = "*140*1*1" + encodedHash;
ActivityContext.startActivity(new Intent("android.intent.action.CALL", Uri.parse("tel:" + ussd))); 

My questions is : how can i prevent this USSD call from changing the orientation?

any help would be Appreciated.