Samsung A401

MarieS3289849  Have you looked at https://help.smarty.co.uk/en/articles/8985136-checking-if-your-device-is-4g-volte-compatible ?

Hi MarieS3289849,

If you do still need help, our customer care team are available daily from 8am – 8pm.  https://smarty.co.uk/contact

Hi MarieS3289849 

If you can send.receive text messages and use data but not able to make/receive calls then you need to check that your handset has VoLTE enabled.
To enable or disable VoLTE on a Samsung Galaxy A401, navigate to Settings > Connections > Mobile networks and toggle the switch next to "VoLTE calls"