Explanation:

✅ Option D: Disable the coupon code. Reduce the basket lifetime in Business Manager to expire some of the existing baskets.
The most effective and least disruptive solution would be to disable the coupon code and then reduce the basket lifetime in the Business Manager. By doing this, some of the existing baskets containing the coupon will expire more quickly, which reduces the likelihood that customers will still be able to use the coupon after it has been disabled. The shortened basket lifetime would help to clear out those who still have the coupon in their baskets, reducing the potential for customer confusion and Call Center calls.

❌ Option A: Disable the coupon code. Clear the production cache from the Business Manager to clear existing baskets.
While clearing the cache might clear some data related to the current session, it would not effectively address the issue of baskets containing the coupon code. The cache clearing would not invalidate existing baskets in customers' sessions, and the baskets would still persist unless their expiration is controlled. This solution might not be as effective as reducing the basket lifetime.

❌ Option B: Disable the coupon code. Email all the customers to not use the coupon code in their baskets.
This solution may help notify customers, but it’s not a reliable way to ensure that customers won’t continue to use the coupon. Many customers may not read the email, or it may be too late to prevent them from using the coupon if they’ve already added it to their basket. It's a reactive solution and could still lead to confusion, especially if customers continue to call after receiving the email.

❌ Option C: Disable the coupon code. Restart the production instance from Control Center to clear existing baskets.
Restarting the production instance might help reset sessions or clear some temporary data, but it is a heavy-handed approach that could cause disruptions for all users, not just those with the coupon in their basket. It’s a more extreme measure that is unlikely to be effective without also addressing basket expiration, and it could result in a negative impact on the user experience.