Arduino MKRGSM1400 how to set the RAT and Band in UMTS mode?

Official Hardware MKR Family MKR GSM 1400
1

Hello
I need to set my MKRGSM1400 for working in to 3G mode for upload a file vs an hosted FTP server, but I noticed that although I have set the band on UMTS the upload speed cannot exceed 2.07Kbs. below is the function that sets this operation in setup().

//Beginning the band manager restarts the modem
  delay(4000);
  Serial.println("Restarting modem...");
  band.begin();
  Serial.println("Modem restarted.");
  delay(1000);
  String newBandName=GSM_MODE_UMTS;
  bool operationSuccess;
  operationSuccess = band.setBand(newBandName);
  // Tell the user if the operation was OK
  if (operationSuccess) {
    Serial.println("Success");
  } else {
    Serial.println(" Error while changing band ");
  }
  String bandName = band.getBand(); // Get and print band name
  Serial.println("Current BAND is: ");
  Serial.println(bandName);

Thanks
Antonio