Hello School_SYSAD,
Generally by adding O365 Calling Plans, you can now use Teams to make and receive phone calls to or from land lines and mobile phones via the public switched telephone network (PSTN). Based on your post, seems both users have no access for Calls tab, so we would like to suggest you to kindly check if you have enable the Calls tab in Teams for the affected users. Users need to have 1:1 calling enabled in Teams and using a Teams client that supports 1:1 Teams calling. To learn how to manage 1:1 calling in Teams, kindly check Set-CsTeamsCallingPolicy.
We also suggest you to kindly verify your calling plan is correctly configuration via this link https://docs.microsoft.com/en-us/MicrosoftTeams/configuring-teams-calling-quickstartguide. If all the settings are correct and still user have provisioning issue, we request you to kindly provide us your affected user email id via the Private Message.
For your privacy, we will send you private message for collecting it.
Thanks and regards,
Ankita Vaidya