Do you have an official written policy for customers that forget to cancel? It could be as simple as "in case you forget to cancel and are later charged, please

Do you have an official written policy for customers that forget to cancel? It could be as simple as "in case you forget to cancel and are later charged, please email us". You could then add a mention to every renewal email. If the policy is not official, but you're already open to reimburse someone that emails you, then make it official. Why have it as a discretionary unspoken rule that lets your customer guess as to the outcome of them asking for a favor.