No data when abroad

Unable to get data when abroad unless in a WiFi zone the option for setting the iPhone 7 Plus is to set the APN on the phone but this option is not available on the phone,Apple support state that it is only available if the carrier allows it but ID say the phone is set to receive data when abroad and I cannot get them to accept that it is a problem that only they can resolve, am interested to hear if anybody else has a similar problem and has been able to resolve it