Yeah this is strange. If they are using, lets say $1000 in credits per day, then they will be charged $700 starting tomorrow. Like you said, they might not even see the email yet.
This isn't the case. If they received this email, it was because they were under the included credits amount. This way, even if they missed the email, they will have six months and we will continue to follow up. If you have a sponsorship, feel free to reach out to me and we can talk about it.