Implement check in setFreeMonth to prevent multiple free months for users

[sourcery-ai]

The setFreeMonth function currently lacks a mechanism to verify if a user has already utilized their free month. This oversight allows users to potentially exploit the system by obtaining multiple free months. To address this, we need to implement a check within the setFreeMonth function that verifies a user's usage history to ensure they have not previously used their free month.

The intended behavior is that each user should only be eligible for one free month, regardless of the number of referrals they make. As an alternative incentive for users who refer others, we can consider offering discounts or other gifts, but not additional free months.

Action Items:

1. Update the setFreeMonth function to include a check for the user's free month usage history.
2. Ensure that the system correctly identifies users who have already used their free month and prevents them from receiving another.
3. Consider implementing alternative rewards for users who refer others, such as discounts, instead of additional free months.

---

I created this issue for @AndlerRL from #320 (comment).

Tips and commands

Interacting with Sourcery

• Generate a plan of action: Comment @sourcery-ai plan on this issue.
• Generate a pull request for this issue: Comment @sourcery-ai develop to
  generate a PR that addresses this issue.

Getting Help

• Contact our support team for questions or feedback.
• Visit our documentation for detailed guides and information.
• Keep in touch with the Sourcery team by following us on X/Twitter, LinkedIn or GitHub.

[AndlerRL]

@sourcery-ai plan