Phone call reminder
On your phone there should be a extra feature so you can add a reminder to call that person back in a certain amount of time. If you said to that person you will call them back in a week you could after the call quickly add a reminders to make that call in a week.
Or you could have a feature on Text message say “call me please “ and if that users is in your Contacts and the phone notices you haven’t called the person it will give you reminders to call.