Cant make or receive calls when traveling to another EU country/roaming

I was traveling to Denmark (EU) from Sweden (EU) where i live.

As soon as i crossed the border i couldn’t make or receive any phone calls.
sms and data roaming works fine, only calls are affected.

I have been in contact with my mobile carrier.
Durring the 2 hour support session we went over:

  1. Making sure roaming is on.
  2. Manuel selecting the carrier network.
  3. Resetting the network settings
  4. Making sure that the APN setting is correct.
  5. Making sure country codes are used before the telephone number like +45 for Denmark.
  6. Restarting the phone in-between changes.

The last thing the support suggested was changing the SIM-Card to a different phone.
I borrowed a Samsung phone and now calls worked. So the support concluded that my Brax 3 phone was to blame.

After the support session i went online to try and find an answer.
Some suggested to try and put the local carriers information in the APN settings. Didn’t work.

I can make wifi calls. but only exclusively on wifi, not mobile data.

At this point i am at a loss and would greatly appreciate help on this topic.